Don't understand your last paragraph. If you bring in some of the older players you suggest, some of whom (Iginla, Sharp) are clearly fried, where would you have the room for the younger players you listed?
It's time to give these kids a chance. Some have had a year in Providence and NHL experience. You can always find a Stafford-type dude later in the season.
This is what people say this every year. Give the kids a chance. See what the rookies can do. Truth is very few coaches are going to let 19-20 year old kids occupy half of the roster. There is probably going to be four wide open top-9 spots available if Spooner is moved/dealt. You will have McAvoy and Carlo on the backend possibly occupying top-4 spots. Pastrnak himself is still just 20. Instead of rookies seeing more playing time, you actually just get elevated roles for for the likes of Nash and Schaller. Or Hayes and Beleskey. There is going to be opportunity for youth whether a veteran scorer is brought in or not. Transitioning 2 or 3 rookies is a lot easier than 5 or 6. Cassidy is going to be about 100% focused on winning, not player development.
I'm not advocating to bring in crappy old veterans. It's not on me to do the research and scouting required to find out who's toast vs who still has something left. I just want to see an experienced player or two added who can clearly slot ahead of the four mentioned (Nash, Schaller, Hayes, Beleskey).