I currently own a dpms ap4 and I'm looking to upgrade to a new upper to help enhance reliability and accuracy. I've narrowed it to either a spikes or bcm considering how well this community receives both, but haven't got much farther .
Bottom line I'd like to know if the extra money for the mid length system is worth it, as well as the extra cost for the BCM vs the spikes. Especially since the spikes comes with a full bcg.

EDIT: I guess its worth adding in that I already own a DD omega 7 rail. Taking the fact that I'd need to get a whole new rail system for a middy kinda puts it in the back seat vs carbine for me (unless its worth it)

You won't go wrong with either one.
It sounds like you are already set up for a carbine. I'd like to try a middy but I don't know that I would take it over a carbine. You do have a longer sight radius and the middy has less recoil from what I understand. But again, I have no first hand knowledge with the middy set up.

I don't think you can beat Spikes for the price and features included.

Kind of answered your own question. As to a choice between BCM and Spikes Tactical, flip a coin.

For the price, Spike's for sure. In the end, your decision might come down to which logo you like better.

I don't know what price range you are looking for, but I just bought this BCM  16" SOCOM carbine upper from Bravo Compnay.  They have a decent sale on BCM uppers with a decent price on the BCM BCG with charging handle when bought with upper ($520.00 + shipping).

BCM 16" SOCOM Carbine upper

It is very high quality.  I have not been disappointed with Bravo Company.

Good luck with your choice.  Either will function just fine.