I brewed a lot of extracts before I moved to AG. Personally, I skipped partials, because I felt comfortable with the processes involved (I later revisited partials, and believe that you can brew excellent beer this way. But imo, partials are actually more effort than full AG. At least with my equipment).
Manticles points are excellent....for the difference to be noticable, you need to be brewing good beer to start with.
If you really want to taste the difference....take an extract recipe that you've done and are familiar with. Preferably one that uses just pale lme/ldme, some spec malts, and a fairly simple hop schedule. Use the spec malts in the same weight, and replace the lme/ldme with enough plain pilsner or ale malt (or if its an English style, use an english base malt, like maris otter or golden promise, etc) to give you the same OG....for the hops, use the same weights as your extract recipe for any late additions, and just adjust your 60 min addition to give you the same IBU you were achieving with the extract. Ferment it at the same temp, with the same yeast.....
then you can compare apples to apples and oranges to oranges. You will have the same beer as your extract version that you are familiar with, but with a base malt in place of pale extract. The differences should stand out like dogs wotsits.
Then you can start rebuilding the grain bill to include proportions of other malt varieties, if you choose to do so, to add more complexity, or to change the beer entirely. Or you can move on to some beers that you may not have been able to do, because extract versions of them are just one dimensional.
edit: fyi, manticle, the attenuation difference is likely due to 2 main things...the significantly higher FAN in grain, compared to extract; and secondly, the ability to be able to control fermentability of the wort by mashing at the temp you want, not what the makers of the extract choose to mash at. fwiw, my 2c is that the FAN is probably the more significant of the two.