Adding hard disks was always the way to go, but very few saw it due to the price unless they truly did the math and a little shopping, even in the very early days.
Case in point: my Mac LC and its storage issue. When I got the machine in 1992, it came with a 40MB drive. That was the more affordable option, and when buying a new system, that's usually a major point of contention. RAM was falling in price and was easy to install, so that part of the puzzle was easy to solve, but storage was at a premium on that drive. A 40MB drive will already be over a third of the way full with a typical System 7.1 installation and Word 5.1 with typical options installed. Toss in MacDraw, Print Shop, Kid Pix, the Apple IIe Card driver, and a few games and the drive is reaching its limit. If there's a big-ticket item like Spelunx to be installed, plenty of programs are going to have to be relegated to floppy disk. Most of my HyperCard stacks were run from floppies, for example.
My dad got tired of hearing me complain about the hard drive being too small. He did his homework and decided a 160MB external SCSI hard drive was the way to go. It didn't have cartridges, but was an effective one-time purchase that would deliver good performance and a decent dollar to megabyte ratio. It wasn't the largest drive available in 1993, when it was purchased, but fit the budget and my needs. The Apple-branded drives were expensive, but the LaCie got a good review and used the same Quantum mechanism. Between the two drives, there would be 200MB of storage, and as a bonus, the LaCie drive came with Silverlining, DiskDup, and a bevy of shareware.
Is it expandable like a SyQuest or Bernoulli? Absolutely not. However, in the end, it had the right mix of storage space, performance, and affordability.
Zip disks came out the following year if memory serves me right, so they weren't an option, but even if they were, this drive probably would have been a little better of a deal. It took years to outgrow it, and by that time, I had an iBook with a 6GB drive sitting alongside the LC. I still have all of the aforementioned equipment, and while I did dabble in Zip disks, the hard drive has outlived them.