While I would never recommend hacking apart an Apple computer that still has functional value to it, some older machines, or MUCH older machines, have aesthetic value.
The Mac SE, for example, is a wonderful platform with an iconic appearance, that offers the facade of a classic Mac. With some internal mounting and hardware work, it could be updated with a LCD panel or (rare to find and CRT displays, even the original, can be very dangerous to work with) color CRT display. Internals that could be used range from an intel Micro-ATX motherboard with a new PSU and SSD, or a Raspberry Pi, or even the borrowed internals of a MacBook Pro or Mac mini (probably the easiest unit to use for this concept technical-skill-wise). Just a forewarning, the rear will have to have some cutting and fabrication work done for ports to look nice and be functional.
One favorite of the PC enclosure hacking community is the chassis of the Blue & White G3, and the G4 towers. This wonderful design allows the mounting of a PC main board with PCI slots on the inside of the enclosure’s door, and has standard mounting locations for hard disks, a power supply, and two 5.25” optical bays. I would suggest these units offer the easiest hardware hack allowing an up-to-date computer in a Mac enclosure.
A final idea: A few days ago I sold an original GameBoy of mine to a young man on Craigslist who is going to be installing a Raspberry Pi and an LCD in its enclosure, to create his own portable game system.
Projects like these for technically minded people can be very fulfilling and fairly straightforward (with good research) and offer a unique and incredibly personal piece of computer hardware to own and use for years to come. It also offers the opportunity to recycle old components rather than buying off the shelf.