did the bolts break at one point?
I have a random after market stand that came with the lug and backside clamp, but my frame still has the original backside welded to it, (even tho the frame tube is a little dented from someone dragging it over whatever snapped the original stand off). The new stand has threads in it that I didn't have bolts for, so I ended up using a smaller diameter of the hardest grade steel bolts I could get and bolting thru both brackets. I try to check it often to hopefully catch it before one breaks, but I haven't got the bike on much of a lean (good for reducing stand stress, but dangerous for uneven surfaces as it almost wants to fall sometimes)
If your bracket fits the curvature of your frame, but just doesn't meet flat to both sides of the welded part, I think that is much better than having a gap around the tube where it doesn't match the arc. at least the directional forces are along the length of the bolt, not across...
the spacer idea may be helpful on the upper side, since that is receiving compressive force while the bottom is experiencing drawing force, as it is now with no spacer I bet you're basically resting on only the bottom bolt when the bike is on stand, and the top one just holds the stand on while you ride. I'd just be careful not to force it out too much and put cross wise stress on the lower bolt, but putting a spacer on the top would probably be a good idea! (not that I'll have much chance to use it myself, but I should too)
