Having a specific accent is useless, too hard and not worth it, unless you are surrounded by that accent most of the time. Learners usually have to deal with several varieties of English (General American, Californian, RP, London, African American, etc.), so it would be pointless to try to speak
exactly like someone from, like, Philadelphia or Edinburgh, when they'll be hearing those accents less than 5% of the time.
It's not easy to make a decision. If you listen to 50% Estuary English and 50% American English, what are you gonna end up using? Mixing them might not be too bad, as far as the phonemes are still distinct. American English with glo'l stops would still be decent maybe, but making "me" and "may" homophones might not be a good idea.