^^^
Production Values: By production values, I mean set design, directing, sound quality/use, visual effects (of course), alien technology/species design....TNG LOOKS LIKE THE 80s. It does. It looks like I imagined an 80s starship would look like. Lots of rounded surfaces, light tans/earthy tones. Aliens look humanoid but not too crazy. Sets look cheaply constructed and things like lighting are overlooked the majority of the time because, well, who thinks that can be important?
In DS9 everything went up, up, up, especially set design. DS9 looked dark and brooding, just like the show itself. Lots of browns, dark teals, and "dirty" colors all around to fit in with the grittiness of the atmosphere. Lighting was used more effectively and cinematography moved away from feeling like a TV show and more to a movie-like experience. DS9 looked great, but it looked NOTHING like the previous Treks. Hell, BSG looks just like DS9! What does that say???
In Voyager, starships finally LOOKED like starships. Colors were cooler and more efficient feeling, panel design and trim more streamlined and functional looking, everything looked futuristic ---- NOT like furniture or decorating from the 90s being used in a futuristic setting. Lighting was used very effectively to highlight different sets, especially the bridge in order to raise or lower the dramatic mood. Depending on the lighting, Voyager either felt like a workplace/governement installation or a home/welcoming environment. In TNG, you never got too concerned because it was always so bright and spacious while on DS9 it took all you could muster not to get depressed by your surroundings and down some Romulan Ale. Oh, and as for camera/shot quality, watch episodes like Timeless, especially when everyone is celebrating the launch of the new Transwarp drive. Voyager took directors seriously.
Enterprise looked like it came from the head of Steve Jobs with that aluminum/brushed metal crap everywhere - it just SCREAMED 2001 (the year, not Kubrik's film). The whole ship felt like you were on the inside of a high-end refrigerator. The cinematography was usually pretty good, mainly because widescreen filming tends to make dramatic shows seem more theater-like (and thus, more dramatic).
Concerning CGI effects, all the series got gradually better, so one can't expect a show from the late 80s to compete at teh same level with a show made 15 years later. BUT, as all those 80s puppet-filled films showed you - if you direct and shoot something right - even if it's just a puppet or a model, you can still get fantastic results. (Look at Farscape!)
As for the majority of your argument... Yes, Voyager was, on the whole, pretty consistent. However, it was also pretty "safe" too. I'd rather see a show like DS9 push its boundaries and try to do something memorable and worthwhile (and risk failure) than to be content giving us the same good-to-mediocre product week-in and week-out (and stay safe).
DS9 was good, but it's a one-time thing. If another Trek tried to follow in DS9's footsteps, people would be like, "Oh, it's just copying DS9". That's the problem with BSG right now. It tried to be so different it actually hurt itself beyond repair. Because the writers and creator kept pushing the envelope of people's expectations for a show after a season or so serious cracks started appearing in the form of "Okay, what now? We can't kill someone every episode!" or "What now? We can't constantly make their life anymore hopeless! Things eventually have to get better, right?"
Star Trek fanboys only think DS9 is the best "Trek" because it is the most non-Trek series of them all. Which is funny, if you think about it. If there was another DS9-like Trek show, you'd see a huge drop in DS9 love. People would probably go back to claiming TNG or TOS is the best. DS9 is a nice expirement in trying something different but besides the name and alien species here and there, it could be ANY sci-fi show out there.
Voyager fits most in line with Roddenberry's original vision of a future where humans try to do the right thing whenever possible, even if that means putting their own lives at risk.
DS9 was all about killing Cardassians, fighting the Dominion and Wormhole aliens. Made for great storytelling but like I said, could have been ANY sci-fi series if you changed the names. I especially liked how Sisko goes from being a nice guy in the Pilot to hiring a hitman in "In The Pale Moonlight"...a great ep, no doubt, but if that's what the Federation is like after a couple years of strife in the Alpha Quadrant, I think I'd rather be lost in the Delta.