After a few weeks away from mission content, I started knocking a few heads together this weekend. Yesterday I completed my 50th Burner mission offer, a Team Hawk effort.
I haven't posted stats the past couple months, mostly because the overall numbers/rates haven't changed dramatically ... and because I've been lazy. :)
Of those 50 Burner offers, I've completed 43 - the others were 5 declines and 2 outright failures early on.
I yield about 14.2k LP per burner. For the completed Burners alone (not including the 174 vanilla lvl4's I've done to yield all those Burners), I've yielded something like 610k LP. If I can yield 1200 isk/lp (and sometimes I don't, but often I do MUCH better), that's 732M isk from Burner LP. Add another ~430M for Burner bounties (about 10M for reward plus bounty where I live), and I am net positive by a healthy amount, despite my initial losses in ships.
Now, this is spread over many months since burners were introduced. But my point is this: if you're looking at return-on-investment for buying up some faction ships and shiny modules, Burners do pay off. If your reason for not doing Burners is based out of the idea that the costs are too high, check your math.
They aren't risk-free. You'll likely lose some ships. But you'll learn some things about ship fitting (I did) and combat mechanics like affects of sig radius and speed (I did). But you'll make some isk, and probably have some fun too.
Now quit declining those Burner offers and go crack some skulls. :)