I've been using file cards to clean files for years, they are absolutely fine. They are designed to clean out a file, and they work as intended. If you are dulling your files from file card use, you probably are using the wrong file for what you're cutting or you're using a file card every other stroke. An appropriate file doesn't clog up nearly as fast when used on what they were intended to cut. Aluminum clogs up a mill ******* file, but that's not what they were meant for. Use an aluminum cut file and the chips just fall out of the teeth. Most of the time, I can just wipe the file across my jeans and the chips fall out, no file card needed.
I would also point out that files are a consumable, and they are intended to be thrown away and replaced when they do get dull from use. I keep boxes of Nicholson, PFRED, Grobet, and Simmonds and Bahco files around the shop, and when they are dull they hit the trash faster than an old kleenex. I'm not wasting time and money getting sentimental about disposable tools. "These rusty old files were my Grandpa's!" Yep, and I have inherited drawers full of old files from my relatives too. I sorted out the good ones and the rest hit the bin. Keep the handles and maybe some weird hard to find ones, then scrap the rest. New files are cheap compared to lost time and energy using old dull files or sending them out for "re-sharpening". Which is simply an acid soak to eat away the teeth a bit and liven them up.
As far as handles, I use Skrooz-On and PFERD and have never had an issue. The Lutz ones loosen up pretty quick, and the SO ones are really nice and comfortable, just triple the price of a PFERD. If that's your jam, keep on shining.
I re-sharpen expensive cutters like carbide end mills, chain saw chain, countersinks, router bits, large twist drills, saw blades, and stuff like that. But a new file is like, $10 and you get months of use out of it. Not worth the hassle to re-sharpen, pop a new one in and keep making money, bill a file to the tooling budget on the job.
If you've got nothing but time and re-sharpening an old file gives you the fizz, go for it. But I would put it up there with washing out fast food cups and re-using take out containers. Why??