In less than 4 years time if you only want a dual-core CPU you’ll be left with the equivalent of a Celeron or nothing; which will mean low clock speeds, small cache etc. If you want a decent performing 2 core system your best bet will likely still be a quad core system. Don’t forget that Celeron moves to dual-core next year and 32nm is only about 2 years away for Intel at which point quad core becomes the norm.
Whether you need the extra cores is another issue but the same goes for graphics memory and hard disk space. A lot of people can still get by with 8MB memory on their VGA card and a 20GB hard drive but even entry level systems have much more than that.