This was fun game on Amiga! I have thought for a long time that this game should be converted to MSX too, so I have had similar thoughts. As a monochrome screen game, Spectrum version looks nice, but I have thought, that as platforms are always moving horizontally only (except lift, which moves blocky way on Amstrad too), there shouldn´t be too much colour clash problems, even better, if each tile next to platform could be always black. So tower background could be monochrome, but platforms should be colourful, hopefully each 8x1 line having own colour to get a nice shiny effect, but even just having monochrome colour which is different than background (=tower) colour, would be nice!

When sprites turn around the tower, simple way to make them disappear/arrive quite smoothly could be as simple as defining few "disappearing frames" for sprites, like these four frames to make 16x16 sprite ball disappear behind the right side of the tower. Each sprite enemy would need few extra frames then, though. But at least it would be a simple way to do that.

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Atari 7800, here you can get some idea, how it could look like on MSX, if tower part gets ported straight from Spectrum, with added sprites

http://atariage.com/screenshot_page.html?SoftwareLabelID=713&ItemTypeID=SCREENSHOT

Amstrad
http://www.cpc-power.com/index.php?page=detail&num=1499

Spectrum
http://www.worldofspectrum.org/infoseekid.cgi?id=0003377

Commodore 64
http://www.lemon64.com/

i think NES/Famicom port is not that bad as reference: https://www.youtube.com/watch?v=8LbqH_4xmoc

Could you please upload screenshot here?  Thank you!