Depends on the political conclusion you think you're fishing for. We could ask another question: how important are foreign affiliates of "first-world" MNC's based in OECD "least developed countries" to first-world MNC's accumulation? The numbers on FDI suggest that the US is by far the favored destination of investment capital, followed by Europe and Japan. China makes up for about 1/2 of the FDI that goes to East Asia, the most heavily favored region for investment outside the US/EU/Japan. Most of the African continent is off the map--a little more than 1% of FDI in '98. Although I don't have numbers broken down by OECD categories of "developed" and "least developed," I would bet that least developed countries aren't all that statistically important to US/EU/Japan's accumulation.
There are other ways that imperialism shows up, of course. IMF and WB policies would certainly be another. But it seems to me that "imperialism," like "globalization," its media friendly double, doesn't do a whole lot analytically in this context, even if it works well as a shorthand description of the tendencies of global capital at this moment. I think it is important to have measures for that sort of thing.
But the more important point is that you'd have to ask this kind of question alongside Doug's question, since "standard of living" obviously appeals to the level on which "class" appears in the US/EU/North to its benighted subjects (ie as lifestyle). If you wanted to mobilize an anti-imperialist politics, you'd have to come to terms with that measure--not as a fiction, but as the "lived reality" of imperialism for many "first-worlders."
All best Christian