There's no need to assume he didn't keep the boost, especially with his durability feats against Pure Boo. I believe someone who desired to surpass Goku would also bother bringing up his loss in power if it were so. All Babidi did was draw out dormant power within Vegeta, not provide him with additional external power, so there's no need to assume Vegeta would be back where he started just by losing his forehead M.