For what it's worth I watched the EU4 prices over 2-3 Steam and PDX sales and the cost was pretty much the same each time, there were slight differences with some of the DLC but it was negligible, so if you are looking to buy it I would just bite the bullet and go for it whilst it's on sale.
PDX released a free update for it recently and are working on another DLC which is due next year, so I doubt the cost will drop significantly any time soon.
I did have the same reservations as you before buying it, but i haven't regretted it for a second, I can easily see how some people have invested thousands of hours in to it
@Panos I've finally finished my Portugal campaign, following your suggestions (although not exactly), was able to take all of Castile's land with the help of Aragon and despite my doubts it was probably one of the most enjoyable campaigns I've done, they certainly do become a power house with a bit of patience