If the springs were heat treated & tempered properly, it shouldn't be a problem. Having said that, if you're a little uncomfortable about leaving them partially open, you might just take them out of the display once in a while, and exercise the springs a little bit. If there are going to be any issues with weakening of the springs, you'll probably notice it while doing that. Or, just periodically alter how they are displayed (sometimes fully open, sometimes closed, other times half-open). I doubt you'll have any problems, though.
The springs on quality knives are built expressly for long-term durability (hundreds of thousands of open/close cycles), so I wouldn't worry about it.