Saying that, it took me only 2 days to work out how to print more than 1 colour. Once you can print 2, you can print 6. If you need help, you can go on a 1 day screen print course to learn - it's not hard.
I've only ever had 1, 8 colour job, but an 8 colour press allows me to keep 3 jobs registered on the press all at once - it saves a BUNCH of time in re-registering jobs.
Most my jobs come in at between 1 and 4 colours, but having 8 has got me a few 6 colour jobs, allows some nice simulated prints and allows me to set up multiple jobs - which is really the handy part. 4 heads means you'll only be able to do cmyk on light shirts, or print 3 spot colours on a dark if they are all underbased. Of course, every printer has different customers, (i don't actually print cmyk right now as I have only had 1 cmyk enquiry in 2 years), but just thought I'd throw in my 2 cents of experience as a full time printer.