I have the same speakers but do not have this problem. Right now I am using a 400 watt amp on mine [CJ 350]. This is overkill; my other speakers need it. I suspect your amp is the problem. I have driven SP 1s with a lot of amps and never had bass problems; smallest was probably a MF A1 25 watt class a. I would get a better amp; the speakers will sound better.
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).