Hi everyone... Need some opinions please.

Recently bought a 2003 WRX saloon and want to stiffen up the suspension a bit. I'm planning on getting the Pedders sports ryder kit in the near future but was wondering if there are any cheaper upgrades I can do in the mean time? The car is completely stock at the moment (suspension wise)

Don't want it too stiff , my front drop links are a bit worn and I've heard swapping my rear ARB out for an STI one is worth doing? Should I install some poly bushes?
Any input welcome

Thanks