My counters to Phil's thoughts...
4150 CMV barrel vs 4140 barrel on the sport
Everything else being equal, the 4150 barrel should last longer in theory... Kinda like 60,000 mile tires vs. 80,000 mile tires... one will outlast the other, but they are both wear items. You decide if the premium for longer wear is worth it.
1:8 twist vs 1:9 twist
Pretty much agree, but if everything else was equal, would choose the 1:8
Mid length gas system vs. carbine gas
*Worthy of consideration*
BCM grip vs A2 grip
Still have the A2 grip on your rifle? A plus if you like the particular grip.
BCM stock vs standard M4 stock
Same answer as grip. It is an upgrade, but only of value if you like the stock.
BCM keymod hand guard with heat shields vs standard guards without heat shields
Worthy of consideration for a plastic handguard... not a big deal.
Again, an upgrade, but only if you like the upgraded hand guard.
M16 BCG vs AR BCG
Agree, but many folks are convinced that they have to change this out.
Upgraded trigger vs standard trigger
A smother lousy GI trigger... yawn.
Smoother is better...
Buffer is a heavy buffer vs. carbine buffer...
Same thought as the BCG
Apples to Apples... given the choice for the same dollar I'd rather have a Sport with a $200 trigger.
But there is enough difference between the two to justify the higher price tag.