Well...........
I don;t think it is the points that lead to lacking diversity, but the will of the character to do everything. And over time, within each gorup, the more limited the scope of the campaign the more centralization on skills you will see from the players. If you never make them use a knowledge skill, how many will actively buy them? EVERYONE has Stealth and Acrobatics, those become mission/combat neccessities. But how many can FIX a firearm? Maybe the odd weapon oriented character, but everyone else just has equipment. if they never run into the need to repair it, why woudl they spend points on skills for repairing it.
Now as a GM you have to be true to your villans also. if in a 250 pt game, all players have diverse skills, but the villans are built 2 dimensional, they will have the power edge on the heros. and the encounters will rarely use skills for resolution, but rely on what the villan CAn do, which is again the powers.
For the players side of things, you have some players that want to do EVERYTHING. When all 4 characters are HTH combat monsters... well, you will have decent fights where they rip your bad guys apart, and then not have ANY way to actually follow clues to solve the crime.
But here is an approach i take to remedy this, even at lower levels.
I built my recent campaign around the idea of the Vidocq Society. People from all walks brought together to resolve crimes. Further, the oiginal Vidocq was a criminal that decided to use his talents to HELP the police instead, and manyt hings we use today (criminal recors and profiles, fingerprinting, etc...) were actually invented by him (or first put to wide use).
But my society wanted specific types to fill their roles. So they are actively recruiting for this, hence I justified in game why i was giving my players some design limitations on their characters. they were also new to the hero system so this woudl keep them from making broken characters withouth getting TOO detailed as to why their ideas woudl not fly. Let them learn the system with balanced characters, and then let them experiment after bcoming familiar with the rules.
So I set up a list of desired agent 'types' the society wanted. like Psychic, Magic, Superior human, Mutant, etc.... your typical origins.
I then had a list of 'roles' that needed filled. there was the martial Arts/HTH Combatant, the Healer, the Taxi to shuttle peopl around, the Brick, etc.....
Now each player coudl pick ONE item from each list. once filled, the Society woudl not recruit more from there.
This is running long, so i will reply to continue........