Is there any difference between imperfect and imperfective aspect?

The problem with all grammatical labels used across languages is that they either lose or add some information. A further problem is that the terms are not used consistently by individual researchers or research paradigms.

So the answer to this question is both yes and no.

Yes, in the sense that perfect is generally applied to tense-related phenomena and perfective to aspect based phenomena (with the proviso that this is not often in the same language). So you're better off using perfect when talking about tenses and perfective when talking about aspects.

No, in the sense, that tense and aspect are closely interlinked phenomena. In Slavic languages they mostly have independent morphology but in Germanic languages, they mostly don't. So the 'perfect' in 'present perfect' describes the same facet of the tense that 'perfective' describes independently.

I once compared the English tense system with Czech to some interesting results. I found a lot of functional overlap but also many differences. Ultimately, using similar terminology was broadly helpful but also with a lot of potential for confusion: http://www.slideshare.net/bohemicus/presenting-aspect-as-tense.