I agree on UPN. Their mishandling of ENT (potentially a flagship show) was emblematic of the poor decision-making that ended in their extinction.I think with as much crap on TV (then as well as now), UPN didn't have to cancel Enterprise...
My personal opinion is that what Enterprise suffered the most from was the "filler episode syndrome." As for bringing the show back, I have long felt that Enterprise should have been brought back in a miniseries format.
The miniseries approach, or maybe a series of TV movies, might have worked, but would have required good promotion by UPN, which might have been beyond them. I think it would have been better if the show had gone to another network. WB, or HBO.