I am in a similar dillema.
I have new Stance Gr + Pro coilovers going into my vert this spring/summer, and I was redoing most of the suspension/brakes in the process.
I've got pretty much new arms all the way around, with the exception of LCAs (might try to freshen the old ones up a bit...), and Hadn't decided on aluminum bushings for the subframe yet...
I was looking at these:
http://www.phase2motortrend.com/ensusupibus1.html
But later found out they are backordered / no longer in production, so who knows where I will find a set of poly-bushings for the S13.
I am going to end up going with the SPL aluminum bushings, and remember that the car I am driving on the road now has a more sportier feel (along with more chassis vibration...).
So, really, are the aluminum bushings that bad, or will it be a harshness you can get use to? I don't want to go bouncing out of my seat if I hit a tiny bump or change in height/levels of the pavement, so as long as it's nothing like that I don't think I'd mind aluminum bushings..