Yes, there were several meetings between Dubček and Soviet leaders and each left Brezhnev and Co more and more suspicious to Dubček's intentions. As altamiro said, USSR feared Czech's defection to NATO, and, I suppose, Dubček could not dissuade their fears. Maybe because it was true at least partially. I don't really know.
If Czechoslovakia allowed to continue and really leave Soviet block, renounce communism, and joins NATO to boot, there will be likely similar movement in all eastern europe, but at this time it would not be peaceful. Regardless of outcome it will weaken USSR more then OTL, it even may collapse in more violent way eventually, though about what time I cannot say.
On the other hand, if Czechoslovakia really only wished to reform and not defect, it could do some good to communist block. At this time in USSR Kosygyn initiated large economical reforms which, some believe, could transform USSR in something like modern China - a real economocal powerhouse, but still with communists in power. After suppressing Czechoslovakia, this reforms were severely truncated, and ended nowhere.