McIntosh tube upgrade - worthwhile?

Yes, I put in vintage medical grade Amprex 12ax7s in my c2300 and it makes a great improvement in lowering the noise floor. As for my vintage mc30 s, mx 110z and MC 240 I use vintage telefunkens in the signal tubes, and some rca black plates in the phono section of the mx110. 

http://www.audiotubes.com 

Brent Jessee

Incredible source of NOS tubes, very nice guy 

You might want to check out Wathen's Cryotone tubes.  Decware is now offering them as an upgrade in their best amps.  At least one reviewer (HiFi Cave on YouTube) preferred their 300B's over the new Western Electric 300B's (which I have in my amp.)

Brent Jesse is great on NOS, though.

+1 for Brent Jessee, huge selection of hard to find tubes. He's not giving them away, but he does have a 30 return policy (with restocking fee), and he does warrant his tubes against failure for 30 days. I've had great experiences with him for 12AU7 family, 6SN7, rectifiers, and power tubes. I've found him to be honest in his recommendations (sometimes preferring a less expensive tube), and he understands which tubes might work better with certain equipment

As a reminder this thread is about whether tubes on a Macintosh amp makes sense to change.

It's not a marketing opportunity to sell tubes.

It may turn out that it doesn't really matter what tubes you use in a McIntosh amplifier.  The amplifier sounds pretty darn good with the JJ stock tubes but could it sound better with different tubes? That's all