Jamie, I am absolutely NOT saying you should be using sand. They are your tanks and do whatever makes you happy with them... But it is fair to mention in response to this that grain size of the sand can make all the difference. The pretty colored sand sold at most LFS's labeled "Aquarium Sand" is typically very fine grained and often causes such problems. Using a larger grained sand will highly reduce the potential for filter damage... also prefilters can be used to prevent sand from ever entering the filter...
Since you had $100 worth of sand I can only assume you bought the over priced "Aquarium Sand", as Pool Filter Sand or other industrial purpose sands (the larger grained stuff) is usually around $4~8 per 50 lbs, making $100 worth or it more than even the most monstrous fish tanks would need.
As mentioned previously
waste is lighter than sand and the gaps between sand particles is smaller than even exceptionally small waste particles
therefore it is unlikely to settle into the sand
The gaps between pieces of gravel are MUCH larger than gaps between sand particles and does allow waste to fall into the gravel. So the problem of waste rotting in gravel causing an ammonia spike is far greater than the same thing happening with sand.
Sure you can gravel vac
but simply put, you will never be able to get all of the rotting waste out of the gravel through conventional gravel vacuuming
then consider the time/effort of siphoning waste off the surface of sand and giving it a quick stir to doing a gravel vac
Its much easier to keep a sand bottomed tank much cleaner
Lastly, I wont quote anyone on this as many posters have made this error
Sand can compact and allow gases to form
it is not true nor fair to say sand does compact and allow gases to form
Myself an many other hobbyists can speak from personal experience that this is an exceptionally rare, yet possible, thing to have happen in a fish tank
and in those rare situations that it does, it is due to user error (typically deep sand beds AND not disturbing those sand beds for an extended period of time).
I agree this thread is just silly
yet I feel compelled to defuse misinformation or poor guidance
I completely agree we can make poor decisions when using sand and cause problems
but the sand didnt cause the problem, the poor decision did
So proper education is the solution, not using gravel
