I take it you meant pre-patched SMW hacks. Assuming the recurring non-varying parts are things like engine code and such, and that the patches don't move any of that (which IPS is notoriously bad for and would require the patches to contain copyrighted data, unlike BPS), a plain ZIP file with one (1) original smw.sfc file and 100 .ips files could give a 7z file with 100 pre-patched SMW roms a run for its money. Probably not overtake it, but it'd be a lot closer of a race.
The bigger issue with compression, especially SCI stuff, is that things like Views already have their own compression (RLE on views for example) and already-compressed data generally tends not to double-stuff all that well. I'm sure there's some techniques that work better in certain combinations, but a zip file, or even 7zip, may not compress all that much if most of the effort goes into stuff like graphics.
That's why zipping a PNG file doesn't do all that much: PNG files already use zip deflate internally. I just tested it myself. Crunching a PNG (just throwing more CPU at the task) reduced my test pic from 53.3 KB to 29.5 KB, half of it by just throwing out the unused alpha. Zipping that saved me all of fifty bytes. All the overhead of compressing away the PNG header reduced it by 200 bytes, but the zip file itself almost undid it all.
Cos one big problem besides solid versus plain compression is that the archive itself requires file headers to specify which file goes where in the archive, its name, checksum, all that jazz. No matter what the exact format is, general-use archives need to know this. The simplest I can think of, .tar, takes 512 bytes per file to describe them and doesn't even include any compression (hence .tar.gz, combining it with a zip-like that takes almost no header at all). Now imagine an SCI resource file. It has its own directory, files have no names or path structures so all it needs is a type, a number, what compression it uses, a size, and for the older versions a volume index. That's all the per-file header overhead it needs. Zip files would be huge if you couldn't get away with like... six or seven files for the whole game -- if those resources were separate files, the zip archive would waste so much space on file headers. Twice, even, considering the central directory at the end of the file!
