While donating does indeed help with the hardware maintenance and other aspects of the server, it doesn't effect the capacity. Since its not a vending machine that says "Insert a 5 dollar bill to increase player capacity by 25". The requirements of capacity increase are ;
Server-end coding ;
Hardware maintenance & stability ;
Over the time, the server capacity will expand as well as the option "an additional server/servers" to be introduced once the stability issues are fixed and can be duplicated for other hardwares.
If you wish to help the game and community itself, there are few options that you can do.
Reporting rulebreaks, reporting bugs, suggestions, mechanics that you are unsatisfied with or wrongly made etc. etc.