Considering the Polo is primary car, and a high hijack/theft risk [I have been there, twice], I agree with other suggestions to sell it and use that towards one car?
120d is awesome. do a dp/exhaust and you not worrying about DPF, and enjoy it.
But if it really is a weekend car, fuel consumption doesnt matter, so why not 135i? Fast, fun, and when everything around that motor breaks you have the polo to fetch parts