Sorry,but clubs don't just hand out massive upgrades because a player plays well,to achieve this from one year to the next would be impossible to budget for.
A club does not play a million under the salary cap on the speculation that some players might have a good year and they need the room the following year to fit in the upgrades.
Managers put clauses in such as mutual option,club option,player option etc...that can be activated but not just because they have a good year.
The amount of players coming off contract each year does not cover it.
If a player is coming off contract they may up the final year to stop being poached before the November deadline.
The reason we don't bring in big names is because we have a good crop of young players coming through and we have budgeted for them,otherwise we would be having to shed contracted players mid contract and we have not been doing that.