We went for our very first time last year, last week of September to first week of October. It was HOT and HUMID! As soon as we would step out of an air conditioned building, the heat would smack us in the face! I'm from Canada, so take my words with a grain of salt as I'm used to much cooler and drier weather!
But it was like being in a sauna. All of our pics show a very flushed, sweaty crowd. The day we went to Epcot was brutal, almost unbearable. We even sat in on a concert of an artist we didn't care for just to be able to sit down!
Now don't think of this as a negative review! It's all in the attitude! I made up a cheesy mantra that I would repeat to myself when I stepped out of a building: "Embrace the heat!" I kept in mind that in less than a month I'd be shivering in the snow at home and this helped me to keep perspective!
A few things to keep in mind and you'll be fine! When you can't take the heat, go on a long indoor ride, even if it's just for the air conditioning. And drink LOTS of water! I didn't force my 8-year-old to drink enough and we had a huge scare and almost ended up in Emergency our last night because of it.
The crowds were fine, we rarely waited for rides (between low crowds and fast passes).. for example, we walked right onto Pirates of the Caribbean both times we went on, etc. This was a really nice surprise as I was expecting lots of line waiting!!
It rained about once per day, but it was not terribly bothersome, we bought a rain jacket to put over our stroller and waited out the rain either under a patio, in the Tiki Room, etc... plenty of places to find cover before the rain stopped.
I never noticed these love bugs you speak of, and I am terrified of bugs and definitely would have noticed!
In fact, the first comment about them: "the love bugs are out and are annoying" I mistakenly assumed was a comment about a higher volume of newlyweds etc being there around that time of year, until a later poster mentioned googling them, lol!
Something to keep in mind which I'm assuming is because of the slow season, is there were not a lot of Photopass people at the parks. More in the Magic Kingdom, but you had to look to find them. I hear you pay a flat rate for all photos and to take as many as possible because of it, but here just weren't many around so you couldn't count on them being around. Also, Hollywood Studios was dead the evening we went, most of the shows had their last showing mid afternoon, so if there are certain things you want to take in, make sure to get to the parks early. Even though one entire side of Hollywood Studios was so empty that it felt like a ghost town, we walked around the corner and the Toy Story ride had several hours long of a wait, and no fast passes left. That's where most of the people in the park seemed to be!
Would I go back again during that time? YES! We had a fabulous time and if you can get past the humidity and just plan to deal with it, there should be very few issues! The thrill of being in Disney World more than makes up for any "drawbacks"!