From Jeff Rowland to Primaluna. Yes or No?

Not in the same league. Look for a better tube amp to provide the refined sound that JR has accustomed you to.

I went from a Jeff Rowland Model 2, to a Pass Labs XA30.5, to a Primaluna Evo 300 Power amp, currently driving a pair of Tannoy Legacy Ardens (93db sensitivity vs the SF's 91db).

I could happily live with any of these amps in my system. I don't think an Evo 400 would be a step backwards provided the drop from 400w to 70w isn't a concern for you. However, it's not a great time to be a tube swapper given the current pricing of tubes. I find the Gold Liion KT-88s and Tung-Sol KT-150s provide the best (and similar) sound in my system. A set of 8 KT-150s could set you back $1500 and they're not the most reliable tube out there. KT-88s would be a good place to start if the stock EL-34s aren't doing it for you.

At home I had Tannoy Kensington loudspeakers, and ended up buying the PL equipment, which although perhaps a no brainer with Tannoy, also was an improvement over the JRDG.  I’m sure there’s some loudspeakers out there that are a great match for the Continuum but for me In my experiences with it I always preferred the PL.  

I had the Continuum S2 and took it to a local dealer to hear Vandersteen Treo CT loudspeakers.  The dealer had them hooked up to Primaluna Dialogue HP amp and preamp with top of the line audio quest cabling.  I was very disheartened to hear the PL sounded so much better than the JR integrated.  It was markedly better.  Perhaps a synergy thing.  If you are curious I would recommend buying a used PL integrated to try in your system while you have the JR on hand to compare - it’s the only way  you’ll ever know for sure.  Even an older model should give you a good idea of how the PL sounds in comparison.  I used to call the Continuum my ‘sonic scalpel’.  It was very detailed and clear, but the PL was much more musical, ‘meat on the bones’, etc. for me, even better bass which surprised me given the class D JRDG.  

Don't do it! The JR is an awesome piece of kit while the PL is good it's just good.

YMMV