I think TNG's effects are perfectly fine as they are. Yes, they're not the CGI 'masterpieces' of today, but they're still high-quality work - I think a lot of what they did with pratical models matches what we do with the CGI ones.
One thing that always bothered me about TNG: all the ship explosions looked extremely fake. There was never any debris field, or even a dust cloud left behind.
(edit: I guess this applies to all the series. For example, when the Odyssey blew up in DS9.)
There was a debris field at Wolf 359.
I don't know anything about the technical aspects of remastering and have no interest in re-done special effects. However, I would hope that HD TNG would be a possibility. If Paramount didn't archive TNG in a manner that would permit this, such an oversight seems to stretch the bounds of absurdity in business decisions.