I'm what you might call a bit of an expert in these matters (Got a BS in Electrical Engineering a few years back) and unless you have a dirt simple rig without much electrical gear (like a Katrina Trailer) a surge protector is a must.
One of the ways to look at the problem is probability & impact.
I categorize camping electrical issues into three main groups...
1) Bad wiring
2) Low voltage / sags
3) High voltage / spikes
Based on my experience, the probability of them happening is #2, #1 then #3, with #2 being the most likely
I would rank the impact at #3, #1 then #2, with #3 being the biggest/worst impact. Caveat - REALLY bad wiring can be really bad :-)
That being said, you want at least a device that checks the wiring and cuts off due to a surge.
If you don't dry camp much and use shore power in campgrounds, particularly in hot weather, you should worry about voltage sags. These are very common as people come/go and cycle their A/C units off and on. Damn near impossible to install an electrical system in a decent size campground that won't have voltage sags and this has only gotten worse with 50 Amp rigs becoming common.
Routine sags that are deep enough will spell trouble for your A/C units and other devices.
So my recommendation is to get a device that covers everything in one unit.
I've been using the 50 Amp model happily for a couple years. When others are in their rigs sweating because the A/C efficiency is crap due to low voltage (so they turn up the A/C and it brings the voltage even lower), I'm a happy/cool camper.