As a lot of forum members will tell you in one way or another: "spend a dollar now to save two down the road." In other words, even if leveling with Bilstein 5100's now is a little more involved than you intended, it will likely save you in the long-run for a number of reasons.
1) If you just do spacers now, you may eventually decide you want something more functional like the Bilsteins. This means you will not only have to pay for parts and labor on the Bilsteins, but you will have already paid for parts and labor on the spacer lift as well. And, you will have missed out on the benefits of the Bilsteins in the meantime.
2) While spacers lifts allow for a larger tire, they don't improve ground-clearance and, as I understand it, they actually decrease the range of up-travel on your suspension, making it less effective rather than more. This could be a problem, especially if you forget that your lift is non-functional and drive it over terrain it's not (or no longer) equipped to handle. I imagine this could lead to costly damage, not to mention inconvenience.
said, your ride will be noticeably better with the Bilsteins than the spacers.
4) Don't risk buying a potentially (read "likely") poor-made product when a proven product exists. I read somewhere (probably on this forum) that a general rule of thumb is, don't buy any brand with the words "Tough," "Rough," or "Lift" in the name, as they are almost all terrible
. FJ owners don't buy "top shelf" because they're snobs or suckers. They buy "top shelf" because they love their vehicles and want them to last.