Thanks for starting this post - I'm a bit frustrated (for our sport) that there isn't anywhere I can find that has any decent info for spectators. Some of what you are looking for can be picked out of the manual provided to teams/participants linked below or you can read through my answers as I've been to the park for 6 other meets over the past few years.
http://www.ncaa.org/sites/default/files/2015_DI_XC_Finals_Participant%20Manual_Louisville_20151027%20%282%29.pdf
What's parking going to be like?
The park has a pretty good sized paved lot - not sure where they overflow but if they end up filling the paved lot I'm pretty sure all the overflow is in grassy areas.
What's traffic going to be like?
There is really only one way in/out (coming in from the north) that they want spectators to use (see map in participant manual) so plan on things getting backed up. I would target your arrival for sometime between 10-10:30 to play it safe.
What's it going to cost to get in?
As others have mentioned $10/person. I have not found anything that addresses children being a discounted rate or free...but would find it hard to believe that they are going to charge $10 for a 2 year old. At least I hope that won't be the case...
How many people are going to be there?
Guessing a crowd of perhaps 5000 including teammates not racing, parents, fans etc...
When would be the best time to arrive?
See above
What's the weather going to be?
Friday overnight low will approach freezing and Saturday's high is forecasted to be upper 40s. Chance of rain Saturday morning plus the wind is going to kick up a bit as a cold front starts to make it's way into the area.
How muddy is it going to be?
The course hasn't seen a ton of rain this fall, but had a couple of days of rainfall this week. I'd be wearing some type of waterproof boot to keep feet dry/warm. However the majority of the course drains pretty well so as a spectator don't expect that you will have to trudge through standing water/mud.
What are the bathrooms going to be like?
Portalets scattered at various locations (near start, near team camps, near concessions). There are also bathrooms located in the recreation building located near the paved spectator parking area.
When do the races start?
Noon Women & 1:00 pm Men
Where are the best places to see the race?
400 m out from the starting line is the most centralized location that will give you a chance to see the ladies 3x plus the finish or the men 6x plus the finish by only moving 100m or so in any direction. Just make sure you know which side of the course you want to be on so you can get to your next vantage point without having to cross the course as you can get hung up if you are on the "wrong" side. Also realize that the majority of spectators will be doing the same so if you are capable of running a bit further you can get to points on the course a little outside this zone where you won't be fighting the crowd as much.
Where are the worst?
Anywhere way out on the 2 loop portions of the course where you won't have a chance to get back to see the runners multiple times. Only caveat here is that if you don't care about seeing the actual finish but would rather potentially see how the race is playing out over the last 1500m the loop on the far eastern portion of the course might be where you want to go as you can see the runners at both the 8300/9500m marks for men or the 4500/5500m marks for women).
What does the "E.P." stand for?
https://en.wikipedia.org/wiki/E._P._%22Tom%22_Sawyer_State_Park