No, you do not need to bother to update them.
It is true that now that heartbleed bug (possibly) has exposed your private key, any third party on network path in between your users and your server ("man in the middle") can see all data as is it was not encrypted.
However, for snakeoil certs, that does not differ much from regular usage case of non-compromised keys, as MITM attack on non-CA certificates is in practice equally trivial. (note that there is a tehnical difference between those two security issues, but in practice they're of the same "weight", so that does not make much difference in real world)
Since you're using snakeoil certs (instead of your own, or some other trusted CA) and so presumably ignore any warnings on such certificates, you should be aware that any data on such SSL connections is really not any more secure than plaintext connection. snakeoild certs are intended only so you technically test the connections before installing real certificate (either signed by your own CA and depending on your PKI - preferable but way more work; or putting trust in some commercial CA, and paying for the less work but lower security)
So in general heartbleed bug has two effects:
- allowing random memory read; which is fixed the moment the apply the security update
- making you unsure if your CA-signed SSL certs are now (security-wise) as worthless as snakeoil ones (and so have to be regenerated and reissued from trusted source). And if you were using snakeoil in the first place, that is obviously non-issue.