Why a person will invest in another cryptocurrency?
it may depends a little bit on the altcoin that you have in mind. but majority of people are investing in altcoins to make profit. that is why you don't even see them looking for a wallet of that coin. they just buy at exchange, keep there and sell there also.
but there are some altcoins such as Monero that have some real world usage too, which means you can use Monero to pay for stuff and reach some higher level of anonymity. [just an example]
What do think will be the features which a person will want in another currency.
that is a different question.
the features are so different. sometimes it is anonymity but it works for some altcoins and don't work for others. sometimes it is staking and the same story and so on.
Do you spend in new coins for the future profit or something else are there which make you interested to invest in a new altcoin?
to be honest i am only sticking to bitcoin and don't care much about anything else. i just trade altcoins and hold bitcoin.