I feel that the two aids are misused a lot, though I realize that in some instances each is very useful. Though I haven't used spurs since I was a kid, I do carry a dressage whip occasionally. That is all I do though - carry it. I never have to use it. I have had to use a whip before I am small, my horse is very large, and sometimes he has a "you can't make me" attitude. If I do use one I use a crop with a very broad flap on the end so that it is more noise and less pain.
I really don't believe in using spurs anymore. I did use them for a short time while I was in lessons as a kid. At the time Horse had decided he didn't want to move any faster than a trot at any time, and that didn't really work with the courses we were attempting. Eventually he got over it, and I used tom thumb spurs to make up for it in the mean time. I disagree 100% with my then-trainer's method. I feel like a lot of big show barns rush people though lessons to get them to the fun part - jumping - to keep them hooked and pouring money into the facility (At $45.00 + a hour it is quite an arrangement for them!). If it had been my student I would have stopped the jumping and gone back to basics and transitions for a while. If that didn't help I would have had the vet out to check for injury, because there was either something wrong with the way I was asking or the way he felt.
I have seen some very stupid people do some very serious damage to their horses with spurs. While I lived in Dallas I was training a horse who had been a general western pleasure horse. It took about a month to see some really promising change in him, and he even looked happier when we rode once he learned to be collected and really understood what I was asking him for. The woman who owned him had an incredibly stupid husband.He decided to ride this horse one night in a play day, and to put it lightly, he spurred the shit out of this horse. I didn't know about any of this until I arrived the next day to work with the animal to find tender egg-sized lumps on his sides, and a pocket of drained fluid on his belly the size of half a Nerf foot ball.
He wasn't in the running for a prize since he'd only ridden that one night, so he'd abused that horse for fun. The horse was right back where it had started once it recovered. Angry and mistrustful - and do you blame it?
I think that the root of my philosophy is this: You shouldn't go to use an aid until you have proven that you can get the animal to do what you are asking for. If you're asking wrong in the first place a whip isn't going to help.