The merit system is excellent as it is in my opinion. It prevents spammers and scammers from creating accounts and flooding the server with unwanted messages.
This is wrong. You can create hundreds of accounts that can be used to spam or scam on the forum. The lack of merits doesn't make it harder or easier to spam.
As it is though could there be a possibility that it could demotivate a long time lurker and take away from the creative process?
Your posting ability isn't affected by the number of merits you have. You can create new threads or reply to existing ones in all sections of the forum expect Serious Discussion and the Ivory Tower.
If someone has been lurking for a long time and has suddenly got a lightbulb moment where they have an excellent crypto related idea but they would have trouble sharing it because they can't easily do so, because of the high barriers to entry.
Again, nothing prevents you from discussing crypto with other members on the forum. You have limitations to the number of PMs you can send and there is a cooldown period in between posts.
Could there be a way to reward lurkers and other people who contribute to the cause while still differentiating them from spammers?
If you are just lurking and reading the forum without posting, how would anyone know about you to reward you? Merits are the differentiating factor between a spammer and a legit user. There are spammers with hundreds of posts without a single merit.
Maybe there can be some fun interactive quizzes or games that test how well someone understands the technology, philosophy and the economics of bitcoin? Would it be a possibility to earn some merit when playing these games?
You would surely get merits if you created such games and shared them with the community. It is possible to earn some from solving them as well, but it depends on if the OP or community believe what you did is merit-worthy or not.
Here is an example of
Bitcoin crosswords that soliton used to make a few months ago.