I like buying more powers at lower ranks -- but then, in D&D, I prefer bards. Flexibility over focus, always fun.
I'd suggest, though, that you make sure you're good at something -- really good -- so that even if your GM hits the party with stuff that you can't hit (or take more than one hit from), you can still be good enough at SOMETHING to be useful.
If I recall correctly, Miss Slick, a PL10 character with 6 ranks of Super Speed (including Mach One Punch with Area and Selective) and 7 ranks of Energy Field (Cold) (which added Protection in and also gave her Touch-Range Slick as a power) wasn't doing as much damage to the bad guys as her more focussed companions... but she had a great time disabling mooks, she required two damage saves, and even if you took her by surprise, she didn't go splat as quickly as most flat-footed speedsters, because she had the redundancy of Energy Field protection (which ordinarily got lost due to PL stacking limits after a few ranks).
So the short answer is: It depends on what kind of bad guys your GM throws at you. A good GM will have enough bad guys that you get some of the action too, even while giving at least one nigh-invulnerable person for your melee masher focused pal to deal with...