I think the worry is way overrated, because as someone else pointed out players will look better next to such a strong nucleus.
We saw the worry last season, all the way up until the Finals among the national media, then after the Finals the national media all of a sudden has hindsight about us having "strong vets".
In 2004, when the Wolves put the combined 67-year olds Cassell and Spree with KG, the rest of the team was TERRIBLE. They started old Ervin Johnson at center (platooned with Olowakandi/Madsen), picked up Trenton Hassell and Fred Hoiberg (both CUT by the terrible Bulls) and put them in the top-6 rotation, and the back-up PG was a series of 10-day contracts through the year. So what happened? KG and Sam formed a nucleus so strong that the role players were able to do their jobs on a championship caliber team. All of a sudden, Hassell and Hoiberg were considered great role players and Johnson became known as the best center in Wolves history.
The point is that quality makes role players look better, and the Celtics have an even stronger nucleus that is also championship proven now. Plus, there's no WAY that the Celtics don't add anybody at all. They filled out last year's roster on the fly starting in August, so they have plenty of time to get that done this year. This "issue" is a non-starter to me.