Upgrade to Simaudio or keep my Classe?

Your components are good and appear to be synergistic with each other. Is there anything specific you are trying to improve on?
The biggest upgrades recently have been in the digital domain and that may be where you will see the most improved performance for your money. I would recommend trying a cd player/dac upgrade to something like Audio Aero Capitole or Electrocompaniet EMC 1 UP 24/192, or one of the other really good units (audition first).
I also own the Alon V's (MkII) and I have enjoyed the improved performance I have received by upgrading to the alnico HF and LF drivers used in the Circe, so that is a direction you might also try. I am currently trying different cables and would be interested in hearing more about the Dragons. I have Alon's Black Orpheus, which are good, but I think there might be better for SS equipment.

The W10 is a most definite upgrade. These are awesome sounding amps which will outperform esoteric amps costing much more than themselves. I once heard them in direct comparison to a Gryphon amp at twice the price and the Sims were as good. Sim audio stuff sounding fatiquing? Please... these amps are top of the line. I suspect it was your speakers or pre that was the culprit there. I have owned Classe 200, Bryston 3B, 4B, Levinson 331 and most recently the Sim W5, and I can tell you the Sim, at least in my system sounds much more musicaL, transparent with a wider soundstage than I have heard at this price level and well beyond. The W10 is again in a whole upper level.
Go listen to them, you must at this price point.

good listening.

I would have to agree with Arkio on this one. I just swapped out my CA-300 for the new Sim Audio W-6 monoblocks. They are a couple grand less than the W-10s, but a significant step up from the W-5. The W-6 are about 1K more than the W-5, but you get a serious 425W/monoblock @ 8 ohms. I also purchased the P-5, but can't give you much info since it hasn't arrived yet. Should be here this week.

Sonics are definitely improved on the W-6. There was nothing glaringly wrong with the CA-300, but I was looking for a more natural/neutral sound, speed, and presence. I got all of them.

When I store demo'd Sim, the system was Eclipse, P-5, W-5, Wilson Benesch Curves, Harmonic Tech interconnects and cables. It was an impressive setup, and I will probably replicate it at home, but felt that the system lacked some power (hence the W-6), and that I might try to find a pair of used ACT-One or Two instead of the curve for now.

If I were in your position, I would take a different path. The Amp seems to be perfectly fine to me therefore, the preamp would be the first thing to upgrade....I would recommend any of the many great offerings from BAT, it will add quickness and sophistication that your present pre does not have. Another great recommendation would be a First Sound Presence Deluxe II, which goes for around 2k used, but it will add great sense of drive and neutrality, albeit never cold. It can compete with really expensive preamps and I am sure it would smoke any Sim preamp offerings sonically. Though the First Sound is very minimalist in priorities, no remote and you will need to deal with a true mono design....switch inputs and volume twice, for the L or the R. Check the raving review at Soundstage. Another thing I would concentrate on is the DAC section. What you have is already outdated, I would recommend an excellent one box solution with 24/196Khs decoding or a separate DAC such as the Bel Canto DAC-2.0 or the much touted, but extremely affordable ScottDixon DAC. I think with these two places to upgrade, I am sure you will find your answer....but if you insist on Sim Audio....check the recommendations of the previous, very knowledgable fellow.

My W-5 blew away my CA-201.