it being formatted to "dynamic" only costs you the need to "import" the "foreign volume" every time you connect it to a different computer.
But converting it without losing all your data will require that data to be moved somewhere else while you are converting it to a simple NTFS volume.
Frankly I wouldn't worry about it.
On a backup drive needing to take that extra step each and every time will act as a safety to prevent you from doing something to that drive accidentially.
In my case the only stuff on my external drive is mp3, mp4, m4v, jpeg and pdf files ("pure data") because my (saved to the hard drive) e-mail is
automatically backed up daily to a pair of USB memory sticks (mounted INSIDE the computer) and my system is "Backed up" by cloning the entire
physical drive the system partition is on every 10-14days.
My problem with "dynamic volumes" is that my system presumes that a dynamic volume is part of a RAID array and whines every time one is connected or disconnected.