I think it's safe to say it would definitely lead to worse traffic getting into the Disney parks.If RCID didn’t exist Disney’s road projects would also need to be added to the long term plans for the counties and ultimately would lead to either higher taxes, other projects getting pushed back or cancelled to cut costs or most likely a combination of both.
On the one hand, the local tax payer doesn't want to sit in traffic.
On the other, they can avoid the roads leading to the parks and likely don't really care if tourists are stuck in traffic.
At least they don't care until it spills out far enough to impact them, or drives tourism down. Both of which take a long time and are much to late for a simple road update to solve.