I line up a bit with Albert86 on the whole need question. My first observation is that the tired spring thing is a bit over sold. I am not saying that all springs don't sag. However, if the springs are made from good quality steel and the design is such that they operate well within the elastic limits of the steel then sag is not going to be an issue. If spring sag and ageing was an inherent problem with springs, then we should all be changing out our valve springs every time we do a TB change.
If you still think that sag might be a problem I would normally suggest checking the free length of the springs. Unfortunately, the service manual does not appear to provide a free length for the springs (that I could find). However, it does provide a ground clearance of 135 mm. The diagram is not absolutely clear; but, it kind of looks like the ground clearance is measured to the mid jack point or the lowest 'thing' in that area. If the clearance on an unloaded car is in that range, spring sag is probably not an issue. You mention that front air dam dragging is an issue. Keep in mind that the NSX payload is only about 450 lbs. If the two occupants happen to be 'line backer' sized, you are likely at or exceeding the payload limits and will be dragging stuff regularly. If you have a payload issue, then a switch to stiffer springs on a higher perch might be an appropriate decision.
Shocks are a wear item; but, probably not as much as people think for modern shocks (minus the tricky magnetic shocks). In fact the aforementioned Bilstein offers (or used to offer) a life time warranty on their yellow body shocks. If the assessment of the shock condition was based upon a push down test on the corner of the car, run from whoever did that test because it is not a reliable indication of shock condition. The NSX OEM shocks are gas charged. If the seals have failed to the point that the gas charge is lost or significantly reduced then replacement is absolutely in order. if the gas charge is intact, I would be less inclined to consider replacement. With high quality shocks and a normally driven car, I wouldn't feel too bad about just replacing a single leaking shock or the shock plus its mate on the same end of the car. If this was a semi serious track car we would not be having this discussion.
You can find the part numbers for your parts from one of the on-line parts vendors such as
https://www.acuraoemparts.com/
If they indicate the parts are discontinued, check out amayama
https://www.amayama.com/en
or spedypartsjapan. I have used both and they can source parts that show up as unavailable in North America. In fact, for me amayama can deliver the parts to my doorstep at a lower cost than any other vendor.
I have used the Bilstein yellow body (HD) shocks on a couple of other cars. Be aware that they seem to come with a fair amount of compression damping which provides for greater transmission of road irregularities to the car. Some people like that sense of increased firmness. I don't. If I want increased firmness I prefer an increased spring rate, not more compression damping. However, that is just me.
If you want to refresh the car, then I might be more inclined to look at the rubber components in the suspension which are subject to ageing. Also, I would only be considering this expenditure if you have already done the other age related things like coolant hoses and the like. Now, if you want to do this just because you want to do it, then go for it.
