Hi Bro,
I don't think that the uneven height is caused by springs.
Anyway, harder springs on stock shocks will shorten shock life.
So far, most here go for either shock upgrade (Koni FSD) with either stock springs or upgrade (Eibach), or go for full coilover solution (Teins / BCBR). If you search the forum, you will find some reviews and can then judge for yourself what suits you the best.