Did the CPL theory route myself, for rather similar reasons.
However I think that it's probably a good idea to do the ATPL's for the reasons you mention, plus there isn't that much more to do.
Also MOST IMPORTANTLY if you don't DO ATPL's and want to do your IR then you have to do another six exams (they let you off HPL). This is the position I find myself in now.
As an aside GTS got me through the last bit of my CPL (fourth sitting for 2 exams) and I'm using them for the IR.
Good luck
PF