>if we do NOT use AC for billing, and do not print CMS forms... what impact will these problems have if we upgrade to 6.6?

By 'these problems' if you mean 'not able to mass print CMS1500 forms' using 'Print All' button then there is no impact. In that case, if you upgraded to 6.5.6 from 6.3.3 then upgrade to 6.6.1 by all means.