You can create two separate wallets if, for example, you want to just have one for you and also your wife. If that is the case you may want to simply use two separate email addresses for all the BOINC projects in order to have two different Cross-Project unique ID's (CPID) to use. Which, are required if you want to get a reward that way. There are many reasons why this is desirable.

However, you could alternatively just put it all in one email/CPID in order to just amplify the reward you can get. That also has it's own reasons why that is desirably better/worse in comparison.

If you'd like, come ask or chat here: https://kiwiirc.com/nextclient/#irc://irc.snoonet.org/gridcoin