Not that important, really

Wear leveling has been made a big issue of, because people are worried about early drive death, but it's just not a complex or expensive process. SSDs remap every page (4 or 8k) from the OS LBA to flash blocks, so they're free to save your data wherever they'd like, and ensuring that blocks are written evenly is simple (compared to other background processes likely to run on an SSD.)

I've used and benchmarked plenty of SSDs, and blocks have failed plenty of times (According to SMART stats) and I've never noticed. That's because blocks have a limited write lifetime, and when a write fails, the drive can just silently re-write the data to another block, and your OS never knows the difference, except for maybe a slightly higher latency. Drives come with varying amounts of spare blocks for re-allocation and to retain a pool of clean blocks for writing, so this block death doesn't become a problem for a while.

The main issues to worry about on an SSD is what the firmware does to maintain a pool of erased blocks, and how they protect themselves against a power failure. If you've got no erased blocks available, then each write has to wait for a block to be recycled, which takes ~50x longer than a simple write to a fresh block. As the drive fills, this is what causes the performance drop that most people worry about. TRIM can help, but the drive still has to be intelligent about how it organizes the data on flash.

Since the SSD blocks are re-mapped, the drive has to store that table somewhere. Since it's expensive to write blocks to flash (Especially blocks that don't get re-mapped, IE necessarily the ones that store the mapping table) they generally store this table in DRAM and only commit it to flash periodically. That means when you lose power (A proper full shutdown is safe,) your drive has a fair chance of losing a few of your last writes, depending on the firmware. I'd personally not consider using a drive without power fail protection (Intel SSD 320, anything with a SandForce 15xx or 25xx controller - Look for pictures of a drive taken apart, banks of SMD capacitors are easy to spot.)