Aside from Rose, who I'm not really convinced is a better option than Campbell or McLean, I don't really think any of our summer signings are taking up positions in the squad that could be filled by the u20s. Even then, the likes of Plummer, Rose, Kipre and Dunne are all only on one year deals. To me, this would suggest that there's scope for Campbell, McLean, McMillan etc to challenge for a place in the first team this year and nail down a place for the start of the next season.
Personally I would like to see us have a core of Scottish players who've came through the Motherwell youth system, but it's not the be all and end all. Inverness won the Scottish Cup and finished 3rd a few seasons ago with 2 or 3 Scottish players in the starting eleven most weeks, with the rest coming from the English lower leagues.