Not really, the best tool for a survey is the one provided by the manufacturer themselves, although not sure how many do any more other than scanny.
Suppose at worst you could do no more than place a panel demo case (Enforcer for example) vaguely in the final location at the property and take a TX to the furthest point, etc...
The explorer IMHO is only of use for troubleshooting after a recurring but intermittent or persistent RF error or alert.
You'll be fine with the right primer and enough sanding...
Last time I went to an open day they were actively encouraging spraying their stuff, although that might have been one specific model...
I think the square Scanny keypads with flap were the best ever design of any company - they did win a (non security industry) award for them to be fair.
Would you be happy using an 18+ year old fridge, microwave, computer, toaster, etc...?
Would you keep a car for 18 years having never serviced it once?
Is your central heating boiler 20 years old?
I would say yes the battery is long dead, your neighbours must love you for that, but I would suggest a newer system for the most
expensive asset you own.
If you are able to convince yourself you will get 'peace of mind' at £200, I genuinely, and this is no joke, would not actually bother
with any of the rubbish you'll get at that price point and spend £10 on a dummy bellbox.
It will be just as effective at stopping a determined intruder as it is at warding off a casual one.
But better yet it will never false alarm, never require servicing, batteries, or the hastle of telling friends and neighbours
how to operate it.