Staggering cap hits works up until a point. At some point, the bill comes due. Both Demaryius and Julius will command long-term deals with huge cap hits that will be unavoidable by at least the 2nd or 3rd year, which is also when we will be in the heart of Wilson, Wagner, Sherm, ET, et al.'s deals.
Yes, Demaryius is better than Decker. However, he will also command way more money. Are you comfortable with paying him Dez Bryant type money? I am not. I don't think he is that kind of player. I could be wrong.
Julius will be more affordable. It's possible they could fit him under the cap. Personally, I think he is a good player but not a difference-maker outside of Denver's system. I wouldn't love the idea of handing him a huge contract. Again, I could be wrong.
IMO, the last thing this team needs to do is hand another $10-14M APY contract to a "weapon" player before he proves anything in a Seahawks uniform. SEA should either keep drafting or hope that Fitzgerald is open to a mid-level, short term deal.