I think you missed the best of the weather. I had marvellous days Tuesday to Thursday (sun, good snow, some ice), but Friday was miserable (rain, fog, very icy, little snow). I ended up turning back less than 1km from the summit of Snowdon due to the driving rain, fog, ice and general exhaustion after 3 big winter days (I was going up from Beddgelert to go a different route - and bag Craig Wen and Yr Aran on the way - I did them at least). I had planned Cadair Idris as one of my alternatives if my chosen routes were off limits for any reason. Luckily I didn't need it, but it's getting close to the top of my list now.
Cnicht and the southern Moelwyns were absolutely beautiful on Wednesday. Definitely the highlight of my trip and I didn't see a single person all day.