Where did you find that it was on the market two years ago as a 4-bed?
In the slightly-better-but-still-not-good old days, Rightmove's website would have allowed you to see previous listings for this postcode whether they led to a sale or not using the Price Comparison feature.
Estate Agents (who are the ones paying RM actual money) didn't like potential purchasers being able to access this information and so it quietly disappeared.
You can still sometimes see old listings on Zoopla, but there's nothing showing on the property timeline on there other than the two Land Registry entries for 2010 and 2003.
Interestingly, Zoopla's estimate is currently showing £616k but this will pretty much only take into account its last sale price and what average prices have done in the area in that time.
So, it won't take into account the loft conversion or ground floor extension that will have added some value.
What often happens though is that at some point, the Zoopla estimate will miraculously change to reflect the price it is being marketed at. Strange that.
Do I think it's worth it? Hell no. Do I think someone will end up paying it? Probably.
In conclusion, a house is worth what you're willing and able to pay for it. Your money, your decision, but as others have suggested, I think you'd be getting more for your money elsewhere.