OP,
I haven't listened to the Spendor D series, so I can't comment on how they compare. But I do disagree that the larger ProAcs are guaranteed to be a problem in your room.
I have a 14x18 room that becomes 12ft wide halfway across the room, with D38's along the 12ft wall, and do not have any bass issues.
I have previously owned the D28 and Studio 140 Mk2 in the same room. In my room, the D38 has better bass control, better driver integration, and less cabinet resonance. They also have more a realistic soundstage, with improved image placement and depth (more 3-dimensional stage). I like the D28 a lot, but it's not a smaller version of D38. They have different driver arrangements, impedance, and cabinet resonance. However, they all share the overall ProAc sound, have great imaging, and not fussy about placement in my experience.
The ProAc D2 is one of my favorite standmounts, but I would go with a floorstander in your room.
I've compared the previous Spendor models to ProAc in the same dealer room, and found Spendor to be less engaging. This has supposedly improved with the D series, but I haven't heard them yet.
I also owned Dynaudio Contour S1.4 LE in the same 12-14x18 room, thinking I should try a smaller/different speaker at one time, and they literally lasted one week before I went to something else (D38). They were also not engaging to me.
I also listen primarily to rock and blues and am very happy with my system overall, but found that cable selection can make a difference in a somewhat revealing system. I'm driving my D38's with Simaudio Evolution Series integrated amp and CD player. I can listen to many rock recordings at levels higher than I care to and the sound is fantastic, and poorer recordings at low/moderate volume due to revealing nature of system.
Sorry for long reply, but I finally found a thread where I may be of use :-)