Speaking as a former WDW bus driver, I think I'll add my two cents...
When I drove, the majority of the time I was silent. I'd welcome guests onto my bus, I'd do the standard spiel, and I'd say goodbye. (During the park exits, if I have a full bus, I add humor to my speil, but the ride itself is silent) But that was about it. Several times, I had guests come up to me and they expected me to sing, or do some routine, and were very dissapointed when I didn't. When I explained to them my reasonings (below) they agreed.
It is actually Federal Law that bus drivers are not allowed to engage in conversation with passengers (or sing, trivia, etc) while operating the vehicle. I totally agree with this law, because driving on WDW property is NOT easy. Lots of crazy unpredictable drivers out there. A driver has to be FULLY focused on the road to be prepared for whatever might be out there. Even a simple conversation is enough to distract the driver enough to cause a potential safety problem.
As unmagical as it may sound, Disney policy agrees with the law; to not engage in such conversation. We have a pre-set dafety spiel that we're to do, however, the only magical interaction that we can have is when we greet our guests. Here at Disney, Safety comes FIRST... it's much more magical to arrive at your destination safe, than to compromise safety.
In regards to bus condition... Narly half our fleet is brand new, or nearly new (116, with 25 more on order). The rest of our fleet (150, give or take) is on average 15-20 years old. Although this sounds old, for a mass transit vehicle, this is not old at all. Many mass transit vehicles can last over 30 years, thanks to good maintenance programs. Disney's RTS fleet are maintained very well, especially when you consider many of them have well over 1 million miles on them.
Every night, each bus is thouroughly cleaned inside and out. Any trash you might find on the bus is from guests on a previous ride who decided to litter. Drivers try and walk the bus every so often, but we don't always have the ability to do such, since we will load immedietly after we unload. (Guests don't like to wait)
Cosmetically, there are some buses that are better looking than others. We're constantly repainting the fleet. In recent years, many older buses have also recieved freshened interiors.
In response to the yellow/red light comment... this is a tricky thing. There are some lights on property (most specifically, the Coronado Springs and the Swan/Dolphin lights on Buena Vista Drive) that turn yellow very suddenly, and then red very quickly. When driving the speed limit (40, 45 respectively), it's extremely hard to stop a bus when that light turns yellow. We have two choices... run the yellow as it turns red, OR, slam on our brakes, send everyone flying forward, and usually end up stopped in the middle of the intersection, often times blocking traffic. This decision must be made in a split second. It's a VERY tough decision, as each situation is different. Me, I always went with the safer decision, even if it meant running the light as it went from yellow to red. (They have a delay for the opposing green)
By all means, I do not mean running a fully red light. By all means, if the light turns yellow, and I can stop, I will. 95% of the time, there will be ample time to stop. But every so often, and those two lights in particular, you have to make that judgement call.
That was ONE scary dude, and he almost went thru a yellow/red light, we almost went flying thru the windsheild! 
I got him twice on my 5 day trip to Disney. 
So forget I mentioned it and let's just say that I remember having friendlier drivers in the past as opposed to this trip and forget it.
I found it!! I won't let it out but good luck to you in your new endeavor! 
I hope your enjoy it!! 
