Or you could get advice from a solicitor. And you could do everything legally like pay your taxes here, register your car here, go on the padron and so on. That way you won't constantly be looking over your shoulder waiting for someone to slap a big bill on you.
Serously, the different autonomous regions can be a pain for things like IHT. They changed in Valencia last August but the initial amount not liable for tax went from about 40k to 100,000 and up to 156,000. Above that it was reduced to 75% of the balance but those over 65 and resident for more than 3 years get a 98% discount. IHT here, if you do it correctly, is virtually nil for spouses and children.
Also assets in the Valencia region still get 100% exemption whilst other areas have reintroduced the wealth tax which applies to property and cash, unlike France where jewellery, cars, fur coats (we have a lot of those in Spain) are counted.
The asset declaration is simply that, a declaration. No tax has (yet) been levied.
But, back to the original post. Hasn't this been done many times? I recall the Daily Telegraph doing something like this a few years ago (think it was something like the Boomerang expats). so you may be able to get a load of research from them.
Like acer, virtually all the expats around us have no intention of leaving. One Norwegian lady returned because of ill health and I know one couple who want to move back as they are missing family.Everyone else is more than happy to stay and limit their visits to UK to a week at a time.
To be quite honest, it is so easy to return back to UK, or for people from UK to visit, that the missing family thing is not really a point now. Interestingly, on another site, one couple went back to UK only to realise that their family's lives didn't revolve around them and are now looking to return to Spain.
Of course, many people do miss the UK and a lot have returned but the main reason is economic. A £600 a month pension giving €900 a month gave a reasonable good living. When it went down to almost parity then just over €600 a month became a struggle. It is also interesting to read how many have returned to UK and now regret it. There have also been people who have been ripped off by banks and builders and they are the ones I feel sorry for. The majority put their trust in solicitors and banks and did everything correctly only to be let down by those who you would normally expect to help you. MEPs are a waste of space. I think fly380 (I've read his posts avidly) would be able to tell you all about that.
But, acer, good news never gets reported. People would rather read about those who have sob stories to tell than those who actually have made a good life. None of us will be on Jeremy Kyle in the near future.