I was under the impression that Blowfish was an encryption cipher, not a hashing algorithm?
Encryption usually allows for decryption, while hashing does not, and I believe Blowfish does allow for decryption. (Although, now that I think about it, I am not entirely sure on that point.)
In any case, the answer to the question of "how much more secure is it" won't have a simple and undisputed answer, as this is a very complex topic.
Lets just say that for the foreseeable future, you will be pretty safe with either Blowfish or a couple of iterations of a salted hashing algorithm, given that you aren't still using MD5 or SHA1 :-]
The reason is that blowfish uses 4Kb of RAM when processing keys. Thus you can make it process a large number of keys, in order to make sure your algorithm uses a large amount of ram.
Say you want to use 1MB for each hashing function. You could generate 1000/4 keys, and feed them into blowfish then rehash. Note this isn't to encrypt the password, you just want to take up 1MB of RAM, so that anyone trying a brute force attack on the hashes requires 1MB for each hash which is unfeasible for them.
You however, can afford 1MB since logins are not a bottleneck on web applications. Things like disk and network IO usually are.