No, Park Hoppers are definitely not a necessity.
I bought them for our first two trips, because I wanted the option of switching parks. We hardly used them. I feel stupid for not knowing I could have upgraded the tix when and IF we wanted to hop.
Knowing that now, I buy base tickets, knowing there's the option to add the hopper later. We have never needed or even wanted to.
Keep in mind, hopping from park to park requires extra travel time.
Generally, the only park we have a dinner ADR in is Epcot, so I make sure to book Epcot restaurants for our planned EP days. Our other dinner ADRs are outside of the parks, so they don't limit us in terms of what park we can visit that day. We don't do that many evenings in the parks, so that frees us up as well. We almost never do lunch ADRs.
I have friends who "always get hoppers". They can't even tell me if they needed them or used them. That's a waste of money.
Some of the best advice I ever got on the DIS was to save that park hopper $$$ until you know you'll be hopping.
The only thing listed in this thread that makes any sense to me as a reason for buying hoppers is if you legitimately want to dine in Epcot every night. Epcot at night is very special, and this makes perfect sense to me. It's a splurge, but I get the appeal.
Short trip? Not a good reason for me. I'd rather limit the number of parks and do them properly, than to barely scratch the surface at any of the parks. That's just me. But I'm not a fan of AK or DHS, so take that into account.