You are correct, sir. The standard Stoner design is DI, or direct impingement system which results in residue being blown back into the bolt and chamber.
Bushmaster makes a pretty good piston kit, form what I hear. Personally I have gone to the LMT system because the barrels and calibers are interchangeable. LMT's aren't inexpensive, however. The advantages are that the chamber and bolt are much cleaner, and because hot gases are not blown back into the chamber, the rifle runs much cooler, resulting in a more reliable, longer lasting rifle. Depending on the system, recoil may also be slightly reduced.
As far as whether or not it's worth it, that is up to you. I HATE cleaning AR's, and I like the technology behind the piston system, so it works for me. If you are just shooting the rifle occasionally then it may not be worth the expense. If you like have the best system available, then go for it. I know your taste in 1911's and an LMT for instance would fit right in
.Edited: Based on the fact that you haven't fired that rifle yet, it would be hard to justify the cost, unles you just want to have it.
Oh, and you can ship the upper yourself, but the BM system is made to be installed easily.