So i bought a M&P 15 about 2-3 three years ago when prices were high. I plan on looking in to a DD or bcm Middy but i was at the right place and time and got a 14.5 colt barrel (1/7) and a colt BCG how much of an improvement is this compared to the higher end rifles. Is it worth keeping around after these mods?
I’m not sure what you are asking. If your asking if the Colt barrel and BCG you bought its better than the M&P’s, well, yes, somewhat they are.
On the other hand the M&P if a fairly well-built rifle in the first place. If I recall correctly the only major thing they don’t do is HPT and MPI their barrels individually. I’m not sure how much you are shooting, but that may not even apply to you. I would leave your M&P like it is and use the new barrel and BCG to build a new upper.
I’m sure you know that the 14.5 inch barrel you have is a SBR if you put it on a upper and lower receiver, right? You need to have a registered lower to do that, unless you pin and weld the flash hider onto the barrel…
Pinned and welded gemtech
Well thats good to know. 
But my original opinion still stands, I would use them to build a new rifle altogther. Keep the M&P as it is.