I too had a C35. It produced what I thought at the time were reasonable 10x8 and smaller photos, but like you I struggled with its limitations. I used the yellow and magenta filters for VC papers and that often produced times in the range of 40 - 80 seconds. And that was at f/5.6 which isn't the best aperture to use for most enlarging lenses. I also found it not that stable so you had to be very careful that you didn't knock it during exposure. Another problem is that the bulbs are now discontinued. If I remember correctly, it took a 50W bulb. I tried a standard 75W bulb even though it told me not to and it kept on blowing. In the end I used a 50W domestic halogen bulb which seemed to work OK.
Still despite these failings, I learnt a lot while using it. But I'm glad I replaced it with a decent enlarger and lens, I really noticed the difference with my first print. There's so many cheap enlargers on eBay at the moment that I'm sure you can pick up a bargain. Go for one of the medium format Dursts like the M670, and get a decent lens, (Nikon, Schneider or Rodenstock) and you'll notice a huge difference. Other makes to look out for are LPL and Meopta -- Ole and others here rate the Meopta Opemus very highly. I've now got a Kaiser (another good make) with a Nikon lens and even using the yellow and magenta filters together my average time for a 10x8 at f/8 is 6 seconds! I now have to use f/11 or f/16 if I want to do some dodging.
Mike