Do you think Bitcoin-based forks (spinoffs) will devalue the original Bitcoin (BTC) over the long term? If not, why? Don't we have too many forks already? Your input will be greatly appreciated. Thanks. 
As the saying goes "Imitation is a form of flattery". However, I don't think this is applicable to BTC though. It is the prime mover obviously, that's why it has a lot of spinoffs, however, it will doesn't have a negative effect, on the contrary it will make BTC stronger as it will get more consensus support from investors. We have seen the majority of the members here, doesn't like fork coins, maybe because of the people behind, or simply that they see it is a "threat", hence they stay with the original BTC.