Eugene's observations

All mains connected electrical equipment worth more than about £10 (the cost of a cheap surge protector) would benefit from having unusual power events (spikes, brownouts, & surges) diverted from them to extend their lifetime or even protect them from total failure.

Surge protectors work by flattening out our irregular power supply usually by use of a metal oxide varistor (MOV) which degrades with each hit it takes.  Each 'suge' above a threshold amount of energy (the clamping voltage) is absorbed by the MOV which acts like an overflow tank to protect equipment from the flood of excess energy.

Surge protectors are sold with an amount of protection - typically perhaps 1000 Joules where one Joule is the energy needed to pass an electric current of one ampere through a resistance of one ohm for one second.  That means they can function for just one hit of 1000 Joules, or 10 hits of 100 Joules, or zero hits in excess of 1000 Joules.

So the quality and price of a surge protector is partly determined by the number of Joules it can absorb.  Once that number has been received the protection is useless - IT DOES NOT FAIL SAFE.  That is why it is essential to periodically confirm how much protection is currently being offered.  

Many protectors have amber lights to indicate that power is flowing, and also green ones the brightness of which indicates the amount of protection.  No bright green light = impared protection.

The other main factor determining quality and cost of a protector is the amount of time it takes to recognise a power event - the fewer milliseconds the better.

So the lifespan of a surge protector is not measured in time but in the number of hits it has taken multiplied by the cumulative size of those hits.  

Also, most surge protectors are power strips with maybe 4 - 8 sockets.  But not all power strips are surch protectors.  The time to check is now.