If you burn CDs with the standard ISO format, it can read them with the appropriate CD-ROM extensions. Usually this implies 7.5.3+.
Personally I think Ethernet is worth the initial cost. Floppy drives are a last resort.
If you have 10.6, you'll need a bridge Mac. I have not been able to test 10.7 support, if it does work with anything it will likely be 9.2 with AFP over TCP/IP only. A bridge Mac is a very useful piece of kit to have, depending on which one you choose. I'd be leaning towards one of these.
The reason you can still write floppies for DOS machines is because of FAT12 support, but that's not to say it will last another 10 years.
Personally I think Ethernet is worth the initial cost. Floppy drives are a last resort.
If you have 10.6, you'll need a bridge Mac. I have not been able to test 10.7 support, if it does work with anything it will likely be 9.2 with AFP over TCP/IP only. A bridge Mac is a very useful piece of kit to have, depending on which one you choose. I'd be leaning towards one of these.
The reason you can still write floppies for DOS machines is because of FAT12 support, but that's not to say it will last another 10 years.