That's a plug in there and it can be removed and replaced with a power valve, they don't come without a provision to add one like my holley 4777.
BTW, the density altitude here ranges from 4500 to 9800 ft., and that's here in Denver. Drive to the mountains and it's a whole 'nother ball of wax.
The DP vs. VS argument is really combination specific and much depends on the ability of tuner himself.