My girlfriend and I were thinking about making love, but I am disabled & have no feeling 'down there', so is it a good idea to risk it?  

Good idea ?Works. Hopefully you are able to achieve an erection. Some paraplegics can sustain prolonged erections. Your girlfriend can have aver pleasureable experience provided you have erections. The attempt will be futile if erections cannot be achieved, in which case you can try viagra (sildenafil) or cialis. So: go for it, just being intimate with your friend by kissing and caressing should be pleasant for both of you.
Probably not. What do you have to risk? You may not sense the stimulis but she may. If you can please her then it is a risk well taken. If you have no sensation how are able to get an erection?