I'm not sure anyone mentioned this yet, but if you have the budget for it, it's worth considering PAYING for WT+ for at least some of your long trips and then looking into upgrading to Club from WT+. It takes the same number of points to upgrade from WT to WT+ as it does to upgrade from WT+ to Club, but it's a significantly better deal (because the difference between WT+ and Club on long-haul is significant). Yes, your ticket might cost about 33-50% more than an economy class ticket but if you can secure an upgrade to Club with points, you're getting that upgrade to a significantly better experience for a relatively small sum.
I also found that my chances of getting an operational upgrade (i.e., free upgrade) from WT+ to Club were higher than my upgrade changes from WT to WT+ (maybe because the WT+ cabin is relatively small - about 40-50 people, whereas there are a lot of people in WT).
I am not sure if it's possible to book separate classes for different legs of your journey but you might, for example, consider paying for WT+ for the overnight portion of a trip and WT for the daytime portion. For example, I would fly WT+ from New York to London overnight and WT back to NYC in the daytime. If there's no real difference in timing (e.g., both daytime flights), then I usually pay to fly in the higher cabin on the return flight - feels like more of a treat than having a plush outbound trip and then having to stuff myself into economy on the way back. For example, if I'm going to San Francisco from New York for the weekend, I'll fly economy on the way there (evening but not night flight) and upgrade with miles to business on the way back (daytime flight).