Ride height will give you some indication of spring wear, but there are other items like worn bushings and bent suspension pieces that can affect ride height. Specific to springs, I think worn pads contribute to the 'thump' you hear when you go over a bump that might have been more muted when the car was new. If the spring keeps the car up at all, I don't think it's worn enough to change it's natural frequency to the extent that you feel vibrations. A rule of thumb that I haven't seen on this forum is to change spring pads when you change shocks. Certainly can't hurt.
Look for a tire shop that has a wheel balancing machine that puts pressure on the wheel. It measures the effect of radial runout so you'll know whether or not the wheel is out of round enough to cause vibrations.
A specialty alignment shop, maybe one that caters to folks who do track events, should be able to sort out your steering and suspension quirks.
In my case, 90% of the wobbles, jitters, rattles and vibrations were fixed by changing from Bridgestones to Michelin MXV4+s. A bigger improvement than replacing 130K mile shocks and dead tie rod ends, IMHO. Maybe you already have Michelins...