It really depends on what you want in the end. If you think that at some point you want a turbo, I'd recommend you buy a GTE, rebuild it and collect all the additional parts needed for a complete conversion; In the meantime you may continue driving around with the GE.
If you're satisfied with the GE then go ahead and rebuild.... only if you must though. Why do you think it needs to be rebuilt?
As for the 70K mi... Well, you'd be amazed what people can do to a car in just 5K. There's also the possibility it was a JDM engine which sat on a rainy pier for 6 months (I am NOT a fan of JDM.... especially when people preach that you just buy it and drop it in blindly). There's also the possibility that whatever issues you're having are related to something which wasn't related to the engine swap; Electrical components for example.
EDIT: Didn't realise who posted this thread. I think you should find out where the problem lies with your current system regardless of what you decide to do down the road... Unless you have another vehicle to drive on a daily basis.
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