I wouldn't expect "low crowd levels" on any Friday during a popular season like Halloween Time, and especially not smack dab in the middle of the 60th anniversary celebration, which is sure to attract lots of visitors for the entire remainder of the year. The crowds early in the day could be manageable and tolerable, but there is a
big difference between manageable/tolerable crowds and low crowds.
In fact, I might expect a lot of people to flock to
Disneyland earlier in the day to get on rides or whatever before the party begins and the park closes to non-party guests. Some people even take Fridays off work and make it a long weekend, so that contributes to crowds as well.
If MHP is business as usual this year, with no major changes to the schedule or to the location of the party (and that is still a mystery right now), I would expect that the earliest part of the day will more or less be manageable and tolerable, but the crowds probably won't be low. When the "crossover time" rolls around -- that is the 3-hour block in which non-party guests and party guests can be in the park at the same time (3 p.m. to 6 p.m. on MHP weeknights, and 4 p.m. to 7 p.m. on MHP Fridays or weekends) -- you will see a big increase in crowds throughout the park.
As Angela mentioned above, people aren't too deterred by the party because they can just head over to DCA.
In my time on this board I have learned to expect the unexpected. Sometimes, when we think the crowds at DLR will be huge they turn out to be manageable, and when we expect the crowds to be manageable they end up being very problematic!
I don't know if this will help, as the comments are mainly MHP-specific (and I still have to add in a few more reviews from the end of the season last year), but in
this post you will find links to a lot of reviews from people who attended MHP in 2014 and in 2013. If you randomly click on some of the Friday MHP reviews, or any of the MHP days (some of which are more detailed than others), you may find some comments about crowds earlier in the day, or even during the 3-hour crossover time.