I'm concerned because blood in the vomit could be from internal bleeding in the digestive tract or it could be from bleeding gums. Given your boy's health and history, I would at least call the vet for input. They may want you to discontinue some of his meds that could be contributing to internal bleeding such as the aspirin. Anemia is not normal in an adult cat...and I would definitely suspect some type of internal bleeding somewhere.
Without being able to examine him, however, one can only speculate as to where the bleeding is coming from. You should always look at the worst case scenario and go with conservative treatment and HOPE that the problem isn't as severe as it could be. I would also check to see if your vet will make house calls or check out using a mobile vet that can come to your home to help alleviate some of the stress your boy suffers from when going in the car to the vet.
Please let me know what they find and if I can help further.
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments