I have a couple of exclusive LEGO sets such as the 50th Anniversary set, 10184 Town Plan, as well as the LEGO Harry Potter 10217 Diagon Alley set. I was wondering if these will increase in value into the future, and if certain LEGO sets increase in value more than others?
Generally speaking, yes. But there are many factors that determine how a given set will be priced over the years. Sets that have rare, more sought after pieces tend to cost more (think monorails), so if you'd happen to have a MISB monorail set you'd be rich. On the other hand, TLG can inadvertently mess with any investment plan by launching sets with similar themes or pieces, making your collection worth just as much as new sets.
Condition is also a key factor, MISB sets are on an entirely different level than opened, used, scratched, faded sets with missing pieces.
For more information i'd suggest looking at BrickPicker. There you can see that while the Diagon Alley has been slowly but steadily gaining value, the Town plan has basically stagnated. This could be caused by the value of a Harry Potter set for collectors, the unique pieces in that set, or any other factors.
There are also other questions in this topic here:
I think anything in excellent condition that is Harry Potter related will go up in value. My cousin has the entire original Lego Harry Potter set, and he's been offered quite a bit for it. Legos are expensive to begin with, and he was offered ten times what he paid.
If sets are popular amongst collectors and AFOLs and not very easy to substitute by other newer sets then yes, generally speaking they increase in value.
The increase in value depends on multiple factors as this Lego investment guide points out:
- Theme and licence: these sets can not be replicated by different brick companies. The theme and licence enlarges the target group of the set significantly. Especially for Star Wars and Harry Potter.
- Minifigures: There are many minifigure collectors which will pay a lot to just get the minifigure from the set.
- Sets from films: fans of specific films are willing to spend more money on sets from a particular film because they associate the film with emotions.
As for both of your sets they increased a lot in value. The 10217 Diagon Alley is now worth around 560€ and the 10184 Town Plan around 360€