Hm, by context I don't think the stuff in Matt 10 is part of the Great Commision but the disciples' "preliminary skirmish" for paving the way for Jesus' crucifixion rather than his second coming. The commandment given in Matt 10 is prior the crucifixion, but the command in Mark 16 is afterwards. I can further explain if you would like
As for the kingdom being "near", I'll admit I'm not sure what Jesus meant. 2000 years really isn't much time compared to infinity, but then you could argue that Jesus should have spoken in the disciples' context. So maybe someone else on the forum can tag this one
About Christians not healing or selling everything to spread the message, I'll have to give a very different story because in my experience, they still do; your situation may be only predominant in the United States or Europe.
The majority of friends I met in Taiwan were missionaries; mostly businessmen who sold their homes and left their jobs to preach the gospel in Asia. Many of them, my parents included, were either PhD's in specific fields or millionaires. They could have lived in the United States and enjoyed their lives, but they decided to invest their time into preaching the gospel in a foreign land an culture. Sure, they're not like in poverty now, but they are nowhere near the upper-class living they had in the United States.
Their children (myself included) go to college only because other Christian communities and relatives support us (meaning that in a way, simply earning cash for God's work is an indirect way of preaching the gospel.)
Why did they not sell EVERYTHING? Well, some did. They did not manage to preach to very many people and instead became a burden to the rest of the Christian community.
The reason is quite simple; it would be less effective. I mean, the idea of selling everything would mean I would sell my computer and run to your house naked and preach the gospel to you instead of type it here...which probably would not be the best way to be a good testimony.
A number of the missionaries I knew did perform "miracles" (sure, you can call it hoax, but it would qualify as a "miracle" if true), some of which I witnessed. In a greater context the reason one may not see it very much is because of media; the same reason we seem to be seeing more earthquakes and disasters now is the same reason we don't see and hear about many miracles.
Displaying miracles on TV has been done before, and needless to say, it was shot down pretty quick. Miracles happen; but because people heed the media more, Christians have concluded that it's a baaaad testimony "showing off" miracles on TV or radio. If that doesn't work, of course it won't be anywhere near as known or seen as say, a movie.