I've always been led to believe (by the hinges) that it was JO sea tour performance as well as your shore tour that were considered the most w/ DH selection and ur dissasociated factored into O5 and CO boards due to their timeing... and if you were an EP player as a JO and went to a community deemed worthy tour you should be ok (provided screen rates don't drop to the low 30% like they did 5-6 years or so ago)...
Have things changed due to the 8yr commitment keeping people around past their shore tours before they can get out?
I'm on the 7yr plan, as with MB. They did try to say I was on the 8yr plan but after producing my OCS agreement, they shut up.
With more people staying in the DH board will get harder. If you do something a few steps off the "golden path", but otherwise had a solid JO sea tour (w/ EP) and a good shore tour (VP-30, VTs, FDNF, etc), you can be fairly flexible on your second sea tour - doing things like VPU or other non-traditional tours is OK. However, if you do something kinda out there for a second sea tour, or you somehow get a drug deal to do another shore tour (very rare), then you're pretty much hosed for DH I would imagine.
I don't know about other communities, but in general, VP isn't terribly friendly to people being adventurous.
IAs are good, but they can't make up for a weak record. If you're an MP out of the first sea tour, or have some other low mark on your record, you're going to need more than an IA.