To assist with cleanup while also making spike traps more lethal just put retractable bridges between the rows of spikes.
Yeah, I think I already illustrated/implied that with how I drew the plans and my recent post and map POI explanations. Why else do you think I said I wanted to take care of the DM-DB before I have to deal with the headache of assigning all the drawbridges?
I intended them to go from _ when OFF, and | when ON to make cleanup easy. And it only applies to levels 2 and 3 due to the amount of dwarves that would be involved in the cleanup, and just the one drawbridge for level 1 to minimize risk for the chained up animals. I mean, notice how in the plans the walls aren't attached to the perimeter of the building? That implies that they aren't normal walls, and also considering they're not Xs, they're not floodgates, therefore they're 1-tile long (but not wide) drawbridges that draw ← thataway, or → thataway.
No matter what, I am railroading invaders to endure this (and a choice of 3 different fates with a forced repeat if they're brave enough via pressure plate and a long walk from up high), and if I have to cleanup while still being attacked (like I'd be dumb enough to do that), I'd be able to choose the path the invaders will have to go. My primary worry, and I'll deal with that when the time comes, of dealing with megabeats/[BUILDING_DESTROYER]s; I might have a legendary military built up by then.
Lastly, why else do you think I allow just a little bit of open space between security features? So I can assign dwarves to stay indoors, and they won't bother going near the main security feature until it looks clear and I give them the "O.K.". Also to ensure that nobody will go near the spike strip until I say so, there's also a reason I'm building it on the top level, and leaving it open. Let's not forget about miasma either. And regarding operation of the spike strip, (SEE New Boiler Design), and I have a good aesthetic spot to place it to make it look like it powers the spike strip.
Sorry if I sounded mean, but I thought my context was clear in my previous posts.
EDIT:
I didn't realize, but considering how it'll all look in the end, when the spike strip is off, all the spikes will be in the up position (and no nobody can get hurt if the spikes aren't moving, nor when dropped on top of them), which would seem rather realistic regarding cleaning up the spikes. We'll just need some sufficiently insane dwarves to do the cleanup... Wait, you mean to say the entire fort is willing to do it? Sweet!
Oh yeah, and regarding the DM-DB, just in case, I made sure to make it so citizens don't trigger the device, so it's still an effective backdoor for anyone who does belong to New Wavehandle, but not those who plan to do wrong with it. Only problem with that is, if I allow citizens to go through the back door, and a Kobold is sneaking behind them, he may accidentally hit the pressure plate before the dwarves, and it'll be fun to watch, but I have a cage trap, as well as some guard dogs and a small wave of trainees waiting for him anyhow if he does manage to bypass security.
EDIT EDIT:
And one other thing I forgot to mention. If you plan on adventuring to this location, I have one special feature that serves as the most effective back-door method of getting into the fort and completely bypass all security (even with the entire place mostly vacuum-sealed from the outside world. But ONLY adventurers can use/abuse this feature if they're clever enough to spot it. In a sense, if reclaiming, but not wanting to damage the landscape, send an adventurer to bypass lockdown and unlock all the doors from inside. Just remember what lever does what.