Is it worth to delete files from SSD drives in order to free up disk space?
No, especially if you need those files.
this free disk space would help to reduce wear of the drive,
Faulty assumption.
Wear leveling encompasses both used sectors as well as unused sectors.
because deleting files will cause overwriting these files with zeroes ("TRIM"), which also causes wear of the drive.
Faulty assumption.
Deleting a file does not cause any (automatic) "overwriting"; that's the reason why files can be "undeleted".
Not does the TRIM operation write zeros to flash. However sectors that have been "trimmed" can be configured to read back as zeros. This is implemented by the on-board SSD controller, and does not reflect the stored data.
Documentation for SSD clearly indicate that the controller will respond with zeros for the data when that flag is set for a "free" (i.e. unmapped) LBA/sector. This does not mean that the LBA/sector actually contains zeros, since that would actually hinder performance (i.e. it's not erased and ready for a write). See the last paragraph of Section 3.8.2 of this Seagete product manual.
I expect that deleting these files will cause such a burst of writing that my drive haven't seen since I installed the system.
Faulty assumption.
Deleting a file only entails the modification of filesystem metadata, e.g. the directory entry and allocation tables. The data sectors of the file are not accessed during a deletion (unless there is somekind of special security protocol in place).
So, in short, what's better for longevity of the drive - to have lots of free space or to reduce mass destruction of files like that?
Neither choice will significantly affect the "longevity" of the SSD.
It's writing (which triggers block erasures) that affects the lifespan of flash chips.
Now you could dream up a worst-case scenario where the unallocated sectors are so widely scattered among the erase blocks that the wear-leveling task has to perform numerous read-erase-write operations (i.e. internal copying) to obtain writable sectors. But such scenarios could only occur after many repeated cycles of writing files and deleting files on a "full" drive.
P.S. I know that having more free space will increase the speed of the drive and my system will run faster.
Only true in the sense that a write operation will not be delayed by unavailability of erased blocks.
The speed of read operations are not affected by the amount of data previously stored.