I find the easiest option is to export, using the option to export each track as its own file. Close the project, change the sample rate, bring the files back in, and SONAR will convert them.

Ah yes! I forgot about that ability - was reading the official workaround and it came across in my head as having to do 16 manual exports to get the tracks I need. So I gave it a go and while not 100% ideal at least you're not totally stuck on the rate you began with. But it would be nice to be able to preserve clip structure and any gain/pan envelopes that are associated, I like the options afforded by non destructive editing! :)
 
Created a feature request thread the other day - see here: http://forum.cakewalk.com/Ability-to-convert-a-projects-sample-rate-m3253067.aspx