I’m new to the forum, and hope that you guys can help me. My family of five are not new to visiting Disney, but we’ve always gone in the month of June (heat, humidity, crowds). This year, instead of going in June, we are planning to try Disney and Universal in December during the Christmas season! We have used the Touring Plans before in June, and boy, what a difference they made! But since we will be staying offsite, will they be just as helpful during this busy time? We have never been to Universal, and I know that they have the Unlimited Express; should I invest? And does making the Fastpass+ reservations shake up the Touring Plans? I will be using the Lines App on my Samsung so that I can get up to date help, I appreciate any advice anyone could give. Thanks! And Happy New Year. 
I love having a Touring Plan. For me, the thing that is most valuable about them is how they adjust my expectations. This is especially true on a busy day! If I only expect to do a few things over a few hours and know what kinds of wait times to expect, then I’m happier.
As for off-site FPP, I think doing a TP will still help. Do the plan in advance so you can see when the wait times start getting really long. Then, at the 30-day mark, when you can make your FPP reservations, set up your 3 FP for the things you can get during those times. You might not be able to get 7DMT or Anna & Elsa in MK, but you will still be able to get good ones for each park. Really! I was changing FP times up until just a few days before our trip, and there was decent availability. Also, more FPs will come available as Disney adds park hours or makes adjustments to things. Get the ones you can at 30 days, adjust your Touring Plans to take advantage of them, and then stalk My Disney Experience until you get the times or attractions that you really want.
It will be great!
I haven’t been to Universal, but hopefully someone with more experience will chime in.
OK, I’m assuming that you used the TPs from the book. As you said, they work, but you need to bear in mind that they are generic plans designed with the average WDW guest in mind, so they will not necessarily be the best plan for you and the days that you will be visiting.
Here is where the Personalized TPs come in. You enter the attractions you want to visit, the day you will be there, and even the times you plan on arriving/leaving, and the Optimizer will design the best plan for you based on projected wait times for that day. This plan will be even more helpful than the generic plan, regardless of whether you are there on a “1” day or a “10”. It also gives you recommendations for FPP reservations, but the process for working these reservations into your plan can be a little tricky, so you might want to check out Making Optimized Personalized Touring Plans with FastPass+ - #48 by Loras
Re UOR and Express Pass, my advice is to make a PTP and Optimize it both with and without XP and see if the additional expense is worth it to you. XP can be very expensive, and many people have found that it is cheaper to book a room at a deluxe UOR resort where you will get unlimited XP and Early Entry into the parks.