At the end of the day, the more cryptocurrency is produced without needed and real usage in economy the lower the value of your crypto assets.
Are you basing this on the supply of a particular cryptocurrency, or the number of different cryptocurrencies which are in existence?
Most projects out a limit on the supply of their base tokens or coins, so only so much can be created, I would not invest in a project with an infinite supply, or one which does not burn unsold tokens.
As for the number of available cryptocurrencies, this matters little as majority of the market is shared among the few at the top of the rankings.
I don't see why having an infinite supply should be a problem.
Let's say for example, you have a crypto-currency that sees its usage (and velocity) grow by 100% every year, and the coins supply grows something like 5-6% per year. Then you won't see an overflow of coins depending on the supply. Plus Blockchains could have a rule, something like : "no activity, no transaction, no new coins".
Same for burning or not, the important part is : Are people dumping the supply below market rate (on a speculator point of view I mean).