SSD is just like HDD , partitioning is not a problem other than it might result in too small disk space. I managed to dual both on a 120GB but then i barely used windows.
The linked post suggests its not a great idea to put swap on your SSD, it doesnt' say partitioning is bad. Swap on SSD is fine , makes suspend/hibernate super fast. It might wear it out a little quicker but SSD isn't designed for long term storage anyway and you should have backups.
USB 3 is almost the same speed as sata so if your usage is uneven then i'd suggest putting the lesser used OS on the external disk.
It really depends on your workload and how much RAM you have , if you are editing big media files and really need the raw speed then nothing will be better than a full SSD install. Likewise if you have less than 4GB of ram then fast disk is essential as you will be swappign in and out of memory a lot.
If you have your OS on the SSD and your Data on the HDD then you will notice when you touch the HD as the system will slow. If its possible to get one system and its working data set on the SSD then it might be the way to go if your really really need performance.