Most rides where you have to leave the
ECV outside do not have wheelchairs available.
I have seen a number of people get a GAC which allows them to use the accessible entrances, even if they do not have the ECV with them. For many rides, this is the mainstream line.
Lots of the rides it says to leave the ECV outside, people bring it in anyway. I suggest getting a GAC and leaving it outside Snow White, Mr Toad, Peter Pan (you can wait in the ECV til you are in front of the line), and Pinocchio. I have seen
ECVs in there and it is IMPOSSIBLE to get them out. You can bring it into the Fastpass line for Roger Rabbit (which is where they often direct wheelchair users anyway), but the standby line is dark and very tight. I would not try to bring an ECV in there.
You will have no problem with the ECV in DCA.
I would get a GAC so that you can use the wheelchair entrances for those four rides I listed (since you cannot see the ride loading zone from where you park the ECVs, so the CMs will not know you have one). Technically you can just tell them you have an ECV, but I think a GAC might smooth things along!