Will this work in my DDR4 or DDR5 motherboard?

No. It is DDR3 and only fits boards with DDR3 slots. DDR3 and DDR4/DDR5 slots are keyed differently and are not interchangeable.

Do I need to enable XMP to get 1600MHz?

There is no XMP profile. The kit runs at JEDEC defaults; check BIOS and set 1600MHz with CL11 timings and 1.5V manually if the board does not pick them up.

Is this compatible with my Intel or AMD system?

It suits mainstream desktop boards that accept unbuffered non-ECC DDR3 at 1.5V, such as Haswell-era Intel and AM3/AM3+ AMD. It will not work in servers or boards that require ECC or registered memory.

Can I use only two of the four sticks?

Yes. Each stick is a standard 8GB DDR3-1600 module, so you can install two for 16GB and keep the rest as spares. Matched pairs in the correct slots are best.

Does it come with heat spreaders or RGB lighting?

No. The modules are bare green PCBs with no heat spreaders and no lighting, which keeps them low-profile for large air coolers.

Is 32GB worth it over 16GB on an older DDR3 PC?

If you run virtual machines, many browser tabs or heavy multitasking, 32GB removes memory pressure. For basic office and web use, 16GB is usually enough and leaves slots free.