That is false economy.not got the £ to replace !
Leave it in, and you will have to do it anyway sooner probably than later, and add more costs because the work that has been done will have to be done again.
Your current systems is extremely wasteful and you are loosing roughly a pound for every one that is available in actual heating. (overall bbu with old cylinder efficiency can well be under 50%)
Tarting the place up before doing the structural stuff is taken care of will double the cost in the long run.
Not to mention the fact that you will have to look at the ugly old thing until it you get a new boiler.