There's definitely benefits to specialized gear for each sport or trip type, but there's also a lot of satisfaction in using a simple, dialed in kit. Putting together an effective gear/clothing system can be a continual process of trial and error, but I've found that when I'm constantly trying out new gear (which I've done my share of) its harder to get to the sort of flow state that I'm looking for in the outdoors.
As someone prone to futzing around and losing track of things, streamlining my gear has made my outdoors experience simpler and more enjoyable. The more familiar I am with my systems, the more they just disappear into what I'm doing. I like to get out the door fast without thinking too much about which combinations of gear that I'll bring for that specific trip.
Its a good feeling to throw on a pack that feels comfortable and to know that it will still feel comfortable after another 20 miles. Likewise, its nice to have a shelter that you can throw up quickly in a storm and know that you'll stay dry and cozy overnight. Developing a relationship with your stuff--using it for various purposes, conditions and environments, is the best way to gain this sort of confidence in it.
No need to feel guilty if you end up buying an extra pack, but it might be worth putting the gorilla (a totally worthy pack) through its paces to figure out what you like and don't like in a pack of that size. Likewise with the duo--that looks to be a very versatile shelter. With wise site selection, that could be your 4 season-wonder-shelter. Or, better yet, buy a TT, a free standing mountaineering tent, three tarps of varying sizes, and sell the duo to me on the cheap :) Realistically, once you've tinkered around and found stuff that works well for you, two packs and two shelters should well cover the spectrum of 4 season backpacking.
Thats just my take on some of the benefits to a minimalist approach on a personal level (setting aside for now the very likely possibility that not buying all that extra stuff is probably better for the long term health of our species and the planet.) Sorry had to go there.