Seems like everyone is reporting higher crowd levels and longer waits than expected right now. Looking at the wait times this morning on the Lines app and I think that my TP predictions are probably way off… 
What do you think of slowing down my walking pace to “very relaxed” on all my TPs to compensate? Would this give me a better idea of how many rides we can realistically accomplish in a given day?
Not really - If I recall correctly, it doesn’t add that much time.
The best thing to do is to make sure that you have optimized/evaluated your TP as close to the date in question as possible, as the TP models are constantly being updated. Also, on the day if your plan starts to go significantly off schedule, use to app to mark what you have done on your plan and then re-optimize it - the engine takes into account current conditions, so you should get a better plan for the rest of the day.
You can create a copy of your plan e modify the date, choose a date with a CL 8, 9 or 10, with the same operating hours. See the significant changes and adjust your “real” touring plan, or make a plan B so you don’t miss anything.
While it will not help too much as @brklinck states, I usually do put my walking pace very slow at high CLs for it is sometimes really hard to maneuver around the crowds even if you do walk with purpose.
Does the touring plan take into account that I will be there on a CL10 day during the week before Easter? My concern is that the plan has very low wait times for most of my attractions. For example, my time for Test Track on a CL10 day at Epcot says that I will only have a 21 minute wait if I go there first thing. That doesn’t seem reasonable? It also says I will have a 40 minute wait for Frozen Ever After at 10:45 without a FP? So do you think the plans take that into account? Or will my plan get totally changed when I actually show up at the park?
Yes, it does. The predicted CL for a given day is based on the projected wait times for attractions on that day, and your plan is using those projected wait times.
The “good thing” about crowd level 10 days is that Disney usually takes that into account and ramps up staffing and capacity at rides. I am going at that time too. I am not as concerned with wait times but you may fall behind with counter service, bathroom breaks, etc. Those lines can be longer. You may want to add in some breaks. I do set my pace to very relaxed.
We did pretty well with our TPs for Feb vacation week. We ran ahead of schedule in 1st couple hours (arriving for RD), but then slower the rest of the day. I think we didn’t account enough for bathroom breaks etc, but it all evened out. I think the best thing is to have a Plan B, knowing what you’d skip if you get behind.