In my opinion, you are way underpowered with the NAD 25 watt unit. I run my Spendor SP1/2E speakers with a McIntosh MC352 stereo amplifier, and I supplement the bass with a REL Stentor II subwoofer. Before getting the REL, I was not happy with the bass response. But I'm happy now. Even with pretty good amplification, the Spendors just don't have enough deep bass to go full range, and so they benefit a lot from a decent subwoofer. So beefy amp, yes, although I've heard others talk about lower-powered tube amps with these speakers. No experience there, so I can't say whether this is true. But I can confirm that having a subwoofer in a Spendor system is the way to go.
Weak Bass from my SP 1/2s
I've lived with Spendor 1/2Es (circa 12/97) for about a year now and love them. However, I have noticed that they just have very low bass output under anything below about 70 Hz (to my ears) though they are rated for +/- 3db at 45Hz. Interestingly enough, my old SP 2/3s, which were smaller and rated down to 60Hz, clearly had significantly more extension connected to the same front end. I have moved them around to no avail and am scratching my head, as I KNOW they are capable of more. Additionally, the woofers move surprisingly little when reproducing low bass at higher dBs levels (less than my 2/3s). Are there any SP1/2 owners out there that have experienced the same thing, and if so is the key a beefy amp? (I am driving them with a 25W SS NAD).