In case #1, if the pressure in the EGR line is higher or lower than expected, the EGR valve will still only be open at part throttle and then only between 1500 and 5000 rpm so neither idle nor maximum horsepower will be affected. However, you may get more or less exhaust gases passing through the EGR when the valve is open. Best case, the ECU recognizes that and adjusts the EGR valve lift to get the right amount of gases flowing through (like the PGM-FI adjusts the fuel injector pulse width to compensate for variations in fuel pressure due to a tired fuel pump or a stopped up fuel filter) so maybe that’s not a problem. If the ECU doesn’t automatically adjust the EGR valve lift, at least it will adjust the amount of fuel injected to get combustion back to lambda 1. So worst case, NOx emissions at part throttle between 1500 and 5000 rpm may be higher than necessary. Personally, that worst case scenario doesn’t make me lose sleep.
In case #2, if the ECU tolerates a large amount of error in the EGR valve lift measurement – yes, that would be bad. Then the valve may actually be open at idle and at full throttle, giving you an unstable idle and costing you horsepower. Looking at the overall quality of engineering in the NSX, I doubt Honda would be so sloppy (then why would they have bothered with a feedback loop at all?) but theoretically I guess anything is possible.
To answer your original question – yes, I did think about permanently removing the EGR valve after reading DAL Motorsports’ notes (see here:
http://ojas.net/nsx/mirror/dal). However, after doing a search on NSX Prime and finding lots of threads on the matter (for example here:
http://nsxprime.com/forum/showthread.php?t=103187 or here:
http://nsxprime.com/forum/showthread.php?t=71768), I decided to leave it alone because the EGR doesn’t recirculate exhaust gases into the engine at full throttle so it’s not going to cost you any horsepower and if I remove it I’ll constantly get a check engine light.
Anyway, those are just my thoughts regarding an EGR delete.