I'd say it's either:
A) Something is wrong somewhere in the amp. No way to tell though unless you take it to a Mesa tech. It's hard to diagnose "awful" and "dull and lifeless" without actually hearing it... which is not your fault, just a downside of a forum.
B) Its just not the amp for you. Have you tried any Recto's outside yours? Again awful and lifeless could just be you looking for a certain type of tone that a certain amp doesnt have. With pinch harmonics a lot go into it outside the amp... more has to do with your guitar and pickups, than necassarily the amp.
Have you tried an OD in front? Not to add more gain but to get a hotter signal. That hotter signal will make any pinch harmonic pop and will add in some mids the Recto lacks. So i think its worth a shot if you havent tried it yet... may be whats missing for you if you like the character of the amp but want a more lively tone.
As far as the crunch goes, in my experience the Recto has a ton and it sounds like you have tried a lot of different settings. So if your lacking it and you have replaced all the tubes i leads me to believe the issue might be something else. BUT just replacing the tubes doesnt necassarily means it would improve the tone... the RIGHT tubes however will make a huge difference.
Lastly like i said in B, it just may be the amp is not for you. I would say if your not up for trying some new "tricks", i would try a whole slew of amps until you find one thats fits you.