I guess you need to do a bit of basic risk assessment. What's the worst someone could do with info and what's the probability of it happening?

Letter might just be enought to be secondary proof of address (instead of a utility bill for example) to set up a bank account. But that doesn't get them the primary i/d stuff like passport or driving licence. And since the address is wrong it wont match voter registration or credit referencing.

Personally I'd be alert for anything untoward for a few weeks but no overly concerned.

Other question is why did DWP get it wrong. Your mistake or theirs? Sent to a neighbouring house with same postcode as you? It's pretty easy to click the wrong house number when using a postcode based address finder.

You clearly need to get DWP to correct their records (maybe easier said than done). But purely on the question of the data getting into other hands, the postie can easily put things through the wrong letterbox when properly addressed.