I've been taking lessons and getting a litlte heavier and crunchier in my style, and that is leading me to alternate tunings. Obviously drop D, but I'm currently playing some things in drop D flat, and we're headed toward drop C.

When I tuned down to drop D flat, my floating bridge started to be noticeably off level. I know I could adjust the spring claw, but then when I tune back up it's going to ride high.

Obviously I could cut out a wood or plastic block and let off the springs, but then if I do want to play with the tremolo...no go.

I've seen these gadgets like the Tremol-No that can "easily" lock and unlock the tremolo, or permit dive but not pull. And there's the tremolo stop lock, which would at least prevent the drop-tuning problem I currently see.

Are any of the gadgets actually useable? Or are they gimmicks that I'll waste money on until I block the bridge?

Are you talking about a capo?

No. Devices to (selectively) lock the floating bridge in place so that it doesn't move in response to string tension.

Example.

A Floyd, Schaller/Floyd, Ibanez Edge double locking tremolos (as well as  on-locking floating trems) all have to be set up completely differently for alternate tunings and/or changes string gauge.  Why I didn't last long with my previous floating trems.  On my last Floyd I put handfitted hardwood blocks on both side of the tremolo block, essentially turning it into a hardtail.  Secured with a couple drops of wood glue so it could be easily reversed. Lots of devices out there, tremel-no and others but if you don't actually use your tremolo, just block it. Alternatively, get a second guitar that's a hardtail. Nice new and used metal monster guitars are cheap these days..,

They work, but I have only used this type: Tremolo Stop

What I ultimately did was just get another guitar without a floating bridge for alternate tunings.

I doubt that that you will find an easy solution that will fit your needs. All guitars, especially those with trems, need to be setup properly for different tunings. Doing Drop D or going to Eb might not be an issue, but lower than that? It's more than just tuning down.....so many variables. Honestly, this gives you a reason to buy more guitars.

However, Digitech has a pretty cool pedal that might work called "Drop". My band tunes to Eb to compensate for our singer. My bassist only has one bass (I know) so he uses this instead of having to tune to the track at home and then retune for rehearsal. It works and sounds great. It tracks well and I have heard no artifacts. I have not had the chance to experiment with it and see how it tracks with guitars chords and distortion (two years later and I still need to borrow it). I have read good things about it from guitarists but have yet to try it myself.

This is a case of wanting to have your cake and eat it too.

What you are asking for - a way to make your floating trem magically rebalance itself on the fly for tuning changes (or string gauge changes, as already pointed out as well) - doesn't exist. At most, you can make it semi-floating, meaning that it rests firmly against a block (or equivalent hard stop) at rest. This means you are dive-only, and have to run enough tension on the trem to keep it clamped to the block/stop at all times when you aren't diving. (Which is more tension than it would have when floating.)

If you want to play in many different tunings, then your options are:

1) A hardtail
2) More guitars
3) Processing/effects

This right here.  If you have alternate tunings that you want to play in consistently then the best course is to keep a dedicated guitar for each one, especially if you want to use a trem.

I'm not familiar with the gadgets, however currently suffering from guitar acquisition syndrome myself, I'm recommending the multiple guitar option.

I was afraid I was going to get that advice.

So I can reference this thread to my wife as a justification for buying a new guitar, right?

Absolutely

Paging Mr. Bigsby to the courtesy phone

Bigsby B50. I change tunings a little bit on the fly without issue.  It won't do extreme divebombs but it will work both directions.

While I guess Bigbsys could be sort of floating because they can be used in both directions, that moniker is usually reserved for trems that are suspended on knife-edges, without any additional support.