Only if you have to take a boat back and forth to the parks. The bugs are terrible on the lagoon and at the boat docks, especially if you plan on watching the fireworks from the boat docks!
we go this time every trip and I've never even packed bug spray....I guess it depends on if the weather is laying a good breeding ground for the bugs. I'd call a CM to check.
I get bitten up in weird places in WDW (fantasmic is one--every time!). Now I just get the Avon sunscreen with bug repellant in it. That way I'm protected and I don't have to carry two things around.
I've been at all times of the year and I've never needed bug spray. (And I live on the humid east coast, so I know from bugs!) I'm pretty sure Disney sprays for bugs.
Also, if you are going to be on fast moving water vehicles, like parasailing, the bugs won't be bothering you there.
I have three big bad bites on my leg. I got them in Frontierland while waiting for the parade last Tuesday night. I don't know what bit me but the bites are still itchy and painful. They ran and bealed for 4-5 days. They still look horrible. I put benedryl and triple antibiotic on them but it didn't seem to help. It might have been some type of fly or a spider. I don't think it was a mosquito. I'm just glad my DDs did not get bitten.