I have been using my Cornet 2 for 4 months now and it sounds really good even though I don't really hear any difference between this and the phono section of my NAD C160 preamp.
If you can't hear the difference between the Cornet (which is maybe not to everyone's taste but is undeniably a very good phono preamp) and your NAD (which makes very good sounding equipment for the $$$ but not known for their phono preamps...) you are either not a critical listener or the rest of your equipment is not resolving enough to differentiate between the two.
If it is the former then don't waste your money and enjoy the tube glow. If it is the latter your money would better spent on upgrading another link in your chain (even stock, the Cornet will NOT be a weak link until you spend significantly more). I am not aware of the rest of your system but if you have a turntable/cartidge that is fairly basic you need to upgrade this first. I have used cartridges ranging from $70 Grado MMs through a Zu Denon DL103R, Cartridge Man Music Maker III up to my current favorite a Dynavector Karat 17D3. The Cornet was able to reveal each change in cartridge and their improvements/weaknesses/strengths and would probably continue to do so as better cartridges were installed (up to a point). A really good cartridge and turntable through the Cornet is magical (assuming the rest of your system is up to snuff) - think of your phono preamp as the optics in a microscope. The better the optics the better the image. However, if the image is poorly resolved or unfocused (as determined by the cartridge and turntable) the final image you view will only be as good as the weakest link in the chain.
Based on my experience, the Cornet will continue to reveal significant upgrades to your vinyl system into $3-4000 (beyond this I don't know and can't afford).
I guess what I'm trying to say is, if you bon't have a really good turntable and cartridge (and a quality interconnect to your phono preamp) spend your money there and worry about upgrading the caps once you go down that rabbit hole

If it is your amp and speakers that might be the bottleneck then the same advice applies. Caps do make a difference, but it will not be noticed unless the rest of the chain is strong enough.
Hopefully this is helpful!