Because if you want to use Maemo 5 as main system then you need to also use tweaks to get gps location to work, to update certs and get imap to work in default mail app. And just for your notice no whatsapp but telegram you can have through pidgin messenger or with telegram-cli as a terminal app. No youtube either except with downloading with youtube-dl for which you need to update certain stuff which may make some other stuff not to work, but that I am not absolutely sure if it breaks anything.

Also you may want to check a thread "Perfect setup for N900" or google "revive N900" which is also in one members signaturew ho has put alot of good stuff of reviving N900.

And there is possibility to overclock the device, take of transition effects and tweak swap usage which all will make the device snappier.

Wellcome to wonderland!