It's a little difficult to say. Surge suppressors have become a consumer good, and they vary widely in quality and what they do. There may be some organizations that certify suppressors for particular applications and a little looking on the web and computer magazines may turn up something. I have some confidence in the protection fault indicators on my suppressors since there was a lot of literature with them, and I know how much I paid. I'd have less confidence if they were hardware store types.
Like KCB says, nothing electronic lasts for ever, but if you don't have some test equipment, the testing probably would cost more than new suppressors.
I'll add a couple of notes about grounding and generators. When I upgraded our electric service, I bought a long line for the service ground. One ground rod is installed near a corner of the house, and the ground line runs around the house to the opposite corner to the second rod. That's a fairly standard technique for installing radio transmission equipment and serves to increase protection from lightening.
The idea is that in event of a strike, huge amounts of current flows from the surrounding ground to a low resistance point (tree, utility pole etc.) and then jumps to the cloud. If the strike is near a house, the current flow can result in lightening jumps inside a house. By supplying a high current, low resistance path around the house, the potentials within the house stay much the same, even though there are huge voltages all around. That's also a reason to make sure your inside copper plumbing, metal drains and well casings are bonded to your electric service panel. I think that's required almost everywhere.
Anyway, I thought it was worth buying the extra line since I already had to install two ground rods. I wouldn't have done it if I lived in a city. City houses tend to be almost surrounded by well-grounded utility equipment anyway. My Brother-in-law did see and feel plasma inside his house couple of summers ago. Maybe he wishes he had my type of grounding.
I installed a backup generator last summer. It's worth checking local codes before you start. Here, backup generators can be hooked into the house wiring only through a transfer switch that has 3 point main breakers. Three point breakers disconnect both hot as well as the neutral service lines. Most service panels have two point main breakers, and the utility neutral can be back fed by improperly connected generators.
My set up is a 60-amp sub-panel fed from an ordinary 60A breaker in my main 200A panel. Most of the house is wired on the 60A(240V) panel. The panel has one main for the utility feed from my main panel and another for the generator feed. Both mains can't be on at the same time. In a power outage, I start the generator, and then throw the transfer switch. Most of the house is then powered. My generator can't supply 60A(240V), but I can pick and choose which circuits are on.
Near as I can figure, that's the best type of code approved generator backup system. Back feeding a stove or dryer outlet works, but is dangerous and illegal here. Before checking the codes, I was looking at some equipment that wouldn't have been approved.