Heartworm prevention is indeed "worth it". Heartworms are terrible. If he won't chew the chewable tablets (they need to be chewed in order to work), ask your vet about getting tablets that you can make him swallow or having liquid Ivermectin doctored up at a compounding pharmacy----you can have it flavored with anything your dog likes, and it costs about the same as the pills. There are other brands of heartworm prevention, too......there might be another one your dog actually likes. My dogs beg for their Heartgard

. There are topicals, too, but if his fur is that thick those might not be best.
The flea meds, though, may not be necessary. Have you had a flea problem in the past?