Permanent move is a bit more complex & expensive. That would count as an import and you'd have to pay import duties and VAT since it was outside the EU. VAT in Spain is ~21%. Additionally since it was homologated for US, you would need to have the bike inspected/modified to pass the ITV in Spain. You need to register it in Spain, so you'd need some kind of permanent address to associate it with. And of course, you would need your insurance setup.
Then the transport issues. I've heard reports of ships waiting to get into ports for 6-8 weeks or more. LA Harbor is one of the worst, but if you aim for Barcelona which is a smaller port, that could also be a factor. Rotterdam might be simpler, but then you need to arrange ground transport from the Netherlands to Spain. The R18 is a big bike, so don't expect shipping to be cheap either. Small bikes could be done for ~$700-1200 depending on the ports, but I'd expect the R18 to be at least double that. Given the shipping delays, prices likely have also gone up a lot.
I wouldn't be surprised if all in between import duties, VAT, inspection/modification, registration & shipping it costs >$10K to do the move. While rentals can be pricy, you'd need to spend more than 50 days renting to cover the cost of moving your own bike & you have ongoing costs of storage, registration & insurance to consider. It is likely more cost effective to buy a bike locally in Spain vs taking a $10K hit on your R18 or just renting if it's not many months at a go you are in Spain each year.
