Ie been on this merry goround also, the more you dip your toes the muddier the water gets.
What seems to be common ground is as follows

1. 5 or 6 years seems the time line for action to be taken on illegal builds from a bulldozers point of view !
2. You can still be fined for an illeagal build after 5/6 years.
3. An legal Almacen will always always stay an Almacen. upgrades not posible to Casa Status sorry !
4. You may pay rates as a vivienda (home) but its still a blikin barn. ( My situation) BASE is quite happy to take your money.
5. Permissions for a new Casa in the countryside are not going to happen ! ( Quote from Spanish Solicitor)
6. Hundreds of thousands of Spanish People as well as us imigrants  live in there Almacens  all year round if it breaks any laws there are unlikely to enforce them and if as I heard some small town mayor or local police jobsworth have in the past a day away from home makes it OK again,
7. Tarragona is taking a much more central role and the tolerance gap for illegal builds is closing by each passing day, examples will be made of illegal builds in the near future.  IMHO
8. It is possible to take an illegal build over 6 years old and have it registered on the escurtura, but will cost a little.
9. I applied for an extension to my illegal  2 storey 100m2 but 14 yr old Almacen properly.... Architects Plans the lot. The  summary was from the adjuntamet.........It appears you already have a big barn why do you need an extension is it because you live in the Almacen and need another Almacen...(yeah busted) if so we think you need to apply for urbinisation ...... which included one of many thing a dinasour fossil survey of my land !
We popped this reply down to the local property solicitor and he summed it up .......DO WANT TO OPEN PANDORA,s BOX .I binned the application !   :'(