If you were Raptors GM would you trade some of those young guys for a star or leave the team as it is?
If the team is left as is, there's a good chance it'll get pounced in the playoffs for the reasons already discussed here. But the team is also set up to be above average for the next 5 years when the dominant teams start to fizzle out, except Boston which has the same competitive window as the Raptors.
If you trade for a top player, there's a good chance the Raptors become the #2 team, but are still miles behind #1. You mortgage that future for a reasonable shot at finals appearance....that lasts maybe 5 games.