Wow, the thread jumped a bit and I only took a day or so offline!
In many ways I agree with you. It is interesting to see the apparent frequency of healings in the days of the early church and the apparent infrequency of healings in our time. I think we need to look at whether there really is a variation and only if we conclude that there is do we need to look at why it might be.
I think that we need to trust ourselves a little more. I think that the desire to see people healed, if that desire springs from the right source, produces an internal tension that is healthy. "You have not because you ask not." That tension brings us into seeking god and relying upon Him.
Leaving aside the time that Jesus physically walked the earth as a man for the simple reason that he was God and neither the apostles of the day nor the members of the modern church can make that claim, we can look at the book of Acts and see examples of people being healed and people praising God for those healings. The question then becomes whether these healings were a matter of routine or something unusual. We need to be careful that we don't look at a condensed account of many years of the early church and conclude that this was the norm - to do so would make no more sense than watching the edited highlights of a football game, seeing a dozen touchdowns scored in the space of 15 minutes and concluding that the game consisted of a touchdown every 75 seconds.
I think this is a valid concern. John writes that there were many more acts that Jesus performed, but he recorded these so that we would believe and believing would be saved. Likewise, when Jesus gives the commission to go out he says, these things will follow those who believe, that they would lay on hand and people would be healed. The problem is that truly miraculous healing is almost unknown in the United States. This is the basis of my belief that healing ought to be more common in the practice of our faith, so that those healings would be a sign to the unbeliever.
We also need to figure whether the truth of the matter boils down to "God always heals", "God heals but not all the time" or "God never heals". These are fundamentally the only three options - either God heals or God does not heal, and if God heals then either God always heals or God does not always heal. From a purely logical perspective we could break down "God does not always heal" into "It's not God's will to heal all the time" and "It is God's will to heal all the time but some conditions aren't met". In the latter of these cases we would need to figure what conditions should have been met.
If we look at the most basic three options I think it's clear from my comments so far that "God never heals" is hard to believe because it only takes one divine healing to sink it. Although there are all sorts of claimed miracles out there that are anything but miracles I personally can't accept that God never heals because of a few things I've seen with my own eyes. That may or may not carry any weight for anyone else but it's enough for me. Likewise "God always heals" sinks if we can find one single example where God didn't heal, and it's not as if we have to look very far to find people who are not healed. We've been back and forth in the thread about Timothy's plight but in many ways poor Timothy is little more than a single data point that everybody can reference equally, in that his situation is clearly recorded in Paul's letter.
So on that basis I don't see how "God always heals" or "God never heals" can be supported by Scripture if we take the overall message as a whole. Which leads us to "God sometimes heals", and whether "sometimes" happens as often as we might expect.
There is at least one incident in Jesus ministry when he passed by a cripple and did not heal him, and there are numerous instances in the Epistles. This eliminates the idea that god always heals. The previous comment, on the great commission, eliminates the premise that God never heals.
If we break "God sometimes heals" into the issue of whether or not we would see more healings if preconditions were met, we need to identify those conditions. This is where we potentially hit an apparent Scriptural conflict, where James appears to suggest that without faith we won't get anything and Isaiah appears to suggest that no preconditions exist at all. If "by his stripes we are healed" refers to physical healing we have to ask why physical healing is not universal, and since no conditions are expressed in the context of Is 53:5 it seems the most obvious conclusion is that "we are healed" refers more to spiritual restoration than physical healing.
I do not think these two passages (Isaiah and James) are in conflict. James postulates that we ought not to expect an answer without faith, yet we understand that there were healings in the Bible in which the receiver did not believe and there were healing in the Bible in which the "healer" was not actively aware. As for Isaiah, I agree that the primary expression of this healing is spiritual. What I don't believe is that it is addressing what would facilitate healing and what would inhibit it. If god chooses, he can heal, yet at times he chooses as a response to something else.
In the case of the diabetes you mention we might ask whether you would just continue the bad eating habits if God were to cure it, although no such conditions are expressed in either James or Isaiah. Logically speaking it's a valid question to raise but if healing were conditional we might expect either James or Isaiah to mention conditions. That in itself is arguably another reason to interpret both passages as relating to one or more of physical healing and spiritual restoration. In many ways the idea that God heals on demand also makes God out to be some kind of half-wit who could just abolish the disease in the first place and prevent us from getting sick at all, but instead leaves us to struggle with stuff until we remember to claim our healing. It looks less like a God who gives good things to his children and more like one of those lame rebates where instead of just paying a lower price you end up paying full price and having to cut the bar off the box, mail it in, and wait for a refund.