I'm the owner of iPhone 4. Is there any possible way to downgrade from 7.02 to one of the previous firmware versions? The whole point is I don't have and have never had SHSH blobs and have never jailbroken my phone. The ideal is to get back to iOS 4, but even 5 and 6 would be fast enough for not annoying me all the time with iOS 7's incredible slowness. If there is some way to do that I will be absolutely happy. Thanks.
Sorry to say that, you can't downgrade your iOS from 7.0.2 to previous iOS versions. Apple won't support this. Not only for iOS 7, but also from any iOS to its previous versions. As you have mentioned that you didn't have SHSH blobs and didn't jailbroken your iPhone, it's not possible to downgrade the OS of your iPhone.
But, you can make your OS faster in your iPhone. Refer this link and do the steps mentioned there to make your phone os speed.