So I am currently trying to gear up my MW Monk, bu I also want to get more BoAs for some low level alts. I can either spend my current JPs on upgrading my heroic items to get into LFR or on the heirlooms. My question is, do LFR bosses give JPs? If so, how much?
If they do, I'll upgrade my pieces and get into some raids. If not, I'll get my final BoA, then focus on getting a higher ilvl.
A good way of getting valor capped is running 5 mans and scenarios - those give quite a lot of JPs. At this stage, you might consider converting them into honour to buy 476 honour gear, as that will help you get the ilevel for LFR.
But in the longer run, using the JPs to buy heirlooms is a very good use of them. They do last, whereas the 450 or 476 gear is soulbound and likely junk in a few weeks. I have pretty much the full set of heirlooms without ever trying to farm them. It's just a byproduct of valor capping my main each week and having nothing better to spend JPs on.
JPs will be much more useful in the next patch, when they can buy old valor gear.