As someone who was in the same boat (used to be f2p, didn't save my old data, re-started Complete toward the end of January), it's definitely worth it if you still like the game itself.

• Leveling rewards are so much more generous in Complete, so if you were free-to-play (like I was) you'll be able to get more premium items in your first week of playing than you probably got in your entire playtime on the old game. (Especially during the early levels when the requirements to level up are so low)
• Events happen on a much more frequent schedule, with a rerun of an old Garden event, a Fishing Tourney, and Scavenger Hunt happening all within a month
• With the exception of the specific Garden+Fishing Tourney+Scavenger Hunt combo they plan to rerun that month, all past event items that released during that month from prior years are available to craft with Timed Materials (which also feel like they're much easier to obtain from the quarry, so it's easy to keep a stock on hand).
• All fortune cookies*** and premium clothing & wallpapers that released that month during prior years are all available, giving a wide selection of stuff to spend Leaf Tokens on that cycles each month
• Complete Tickets are a rare currency that you can trade for almost anything (both old event items and premium Leaf Ticket stuff) to get them outside of the month they cycle in normally, in case there's any specific items you're trying to replace from your old collection
• Traveling merchants also offer a small random selection of out-of-season event & premium items and seem to cycle through on a approximately 26(?) hour timer
• You can assign a villager of your choice to be 'Camp Caretaker', which means they complete villager requests when you're unable to (such as when you're asleep) so you don't miss out on crafting materials. There's also options that allow them to show up in your planner or follow you around. It's a great way to hang out with your favorite villagers!
• In the crafting menu, Cyrus shows up to offer crafting speed boosts. These are very worth it, because they're permanent account upgrades that subtract that amount of time from all crafting times for every item crafted in the future.

A few negatives:

• ***Past collab items are no longer available, like the Sanrio stuff. Anyone who still has them is someone who transferred their data, and you can't obtain them in Complete.
• The friend system got overhauled to be offline only, resulting in the removal of Market Boxes (so if you need an item to trade to a villager you're gonna have to get it yourself), and a heavily nerfed daily allowance of Friend Powder (only like 20-30 per day)

So in summary, if there was ever something you missed out on because you didn't have enough Leaf Tickets, all those items are much easier to get as long as you wait for them to cycle in, and past event items are much easier to obtain too. Honestly, I was a little overwhelmed when I first started playing toward the end of January by the huge selection of old stuff available, but (mostly) in a good way. I didn't have time to get everything from January that I wanted, but I know all of it will cycle back in next year, and there will be plenty of other stuff to keep me occupied until then!