Suspension and tire question

MaysEffect

You may have already bit the bullet on doing this.

But in either case, if you have the tools to do it, its a rather straight forward and relatively simple task to do. Having a lift makes it about 50% easier, but not necessary at all.

There are several tutorials and install videos online of doing it on stands in a garage, very few horror stories. Buying the tools necessary is equal too if not less than paying someone else to do it. And most of the cost comes from a good torque wrench and jack. If you buy the run of the mill harbor freight stuff you can get everything you need for under 500 bucks, which is the typical cost for a "professional" install, give or take $100.

The rear is significantly easier than the front as the damper and spring are divorced. The key to a easier install is to preload the lower control arm by using your jack under it and then loosen the bolts.
Before removing either the spring or shock, remove the ASB endlinks from either the control arm or ASB, this will reduce the amount of pressure from the opposing wheel.

Again probably already solved, but that amount of mileage does not warrant a change in dampers without internal damage. In the case of what Boss_302 suggested, this would not warrant tire bubbles or damaged sidewalls either. In most cases it would be from under-inflation (dropping below 30psi) or over inflation while hitting a bump at the right angle to pinch the sidewall or indent it. Bubbled on the inner sidewall usually comes from over-inflation and a bump hard enough to displace enough air to blow the sidewall out.

Without pictures it's all guess work.

Deteriorated piston seals and worn inner tube lining would increase oil flow. As Boss302 stated it would allow the tire to oscillate more and cause vibrations, but this would in almost all cases not increase the chances of tire deformations. This would come from either a compressed shim stack or blockage in oil flow, which is a increase in pressure. This mostly comes from the damper bottoming out and denting the piston shaft, jamming the seals and nuts securing the shim stack. The increased resistance would promote a harsher ride and reduce the ability of the tire absorbing and deflecting road shock. As a result, the tire sidewall is doing the job of the damper. Odds are if the damper is damaged, its from the damper bottoming out and pinching the flow of oil. Over time excess blow by will cause the ride to get softer and less controllable, but this will take a very long time, or extremely wavy and bumpy roads. And you'd have to hit every major bump.

This is all an assumption that the damper is actually damaged. Although it may compress without oil squirting out or making noises. A sign of damage is if you feel any sort of click or swift bump in any point of the compression and rebound when compressing it by hand. I'm going to say that this is not from damaged dampers considering you said both tires. I'm more inclined to believe this is solely tire related problem.

The s-tune(nismo) damper and the base model damper literally have the same valve and shim stack design, they differ in the fact the nismo version has a slightly smaller bumpstop and different spring rate and length. Buying the shocks without the springs would be no different than buying the base variant. An unnecessary increase in cost if any difference in price.

p.s - sorry for errors, i didn't proof read.