The dialogue in "Balance of Terror" can be taken to mean that the cloak was of an improved type. As for the looks of starships in Enterprise, I'm not too disappointed, I know some people who would have been disappointed if the Romulans didn't have the coolest design yet. Though they could have used the Bird of Prey from TOS, but they decided on a new design. Hopefully, the next time we see the Romulans, they may indeed have the Bird of Prey, I'd like to see them give it a "big-budget" make-over like they did for the Klingon battle cruiser. Or make a smaller precursor, maybe call it a Warbird or War Eagle, or War Hawk. Who knows?
In "The Minefield" I never saw the Romulans warp, only cloak, and evidently the minefield had been there for quite a while and had a slightly less sophisticated cloak than the Romulan ships, which they couldn't detect, IRC. Maybe I'll get the tape out and watch it again.
The Phase Pistols don't bother me too much, I just figure that Starfleet went to lasers because they went to war with the Romulans in a few years and lasers were more powerful and less expensive/easier to produce than Phase pistols. And don't forget the phase pistol is not as powerful or versatile as the much smaller phaser-1 from TOS.
"Retreat?! Hell, we just got here!", annonymous American Marine, WWI
"Gravity is a harsh mistress....", The Tick