If you call "constantly" about 10 years between tube changes.... no they do not need constant change. nearly all ss amp guys I know have bought several new amps in that time frame.
Sorry, but even the D800 doesn't sound anything like their tube amps. I bought one, it sounded absolutely nothing like my Strategy or my Bass 400, and couldn't even cop the glassy high end of a tube amp.
Agreed on all of the above - I've played thru a D800, and although it's a killer amp that I will eventually own, it doesn't sound like my Bass 400, nor does it cop the tube vibe nearly as well as my Streamliner 900 does...