I don't think it will make you any more money directly but a well researched and presented lore can most certainly increase the power of your fanbase and franchise. Just look at the power that Lord of the Rings has.
That said remember that its only going to be a smaller percentage of your customers who will come to your website; who will read online and who will interact this way. That said they are more likely to be the most keen of your fabase.
Personally I think its a good idea, esp with the fact that things like Kindles still handle images and maps very badly. So a website with a neat map is a great idea.
A few considerations:
1) Spoilers - try to avoid them. A map might well change over time as a story develops, so its better to try and stick to the map being historical and/or at the start of the series. This way you reveal fewer spoilers to your potential readers.
If you got more advanced you could have map settings that allow the reader to view the map/info at different stages in history in your series. Letting you show earlier ages; but also spoiler containing latter series developments (with a suitable warning for readers so that they make a choice and don't accidentally stumble upon things).
2) Even if you don't use it publicly, the background that goes into writing it out formally might well help you as a writer keep track of your own created world and what is going on within it. So this is not a wasted opportunity even if you don't put it to full use.
3) Artwork - bad art fails, good art sells. How you artistically represent the map and your world is important. This is one aspect that might make this more expensive or time consuming; it could also be the kind of thing that makes this more of a backstory/reference for yourself; Vs something that you display to your readers.
4) Depending how much info you put into it keep in mind that it exists. Last thing you want is to wind up working to altered versions of the lore/history of your world and leaving up old bits that are changed.
Edit forgot to say - if you do this remember - stick the link in your book and try to make it super simple (the title of the series; the world setting; your name; etc... ).
