I'd go for it but it all depends on your riding schedule and the kind of riding you do.
If you're just doing short day rides of 250 miles or less you should be able to monitor your wear at every rest stop and watch for noticeable deterioration. It's the
T-CLOCS safety check refresher
If you have a big enough trip coming up soon of 500+ miles or you live in a rainy area you'd probably want to consider changing it soon.
I kind of have doubts over the assessment that 40% tread left = 1,000 miles left. Perhaps they're measuring to the wear indicator.
At any rate I personally run both of our bike tires down to the tread wear indicators and replace shortly thereafter. I'm old enough and make (just) enough that delaying the cost of a tire replacement by a couple weeks/months doesn't justify the risk of tire failure. We're going on 700+ mile trips every month between April-October so I've got to stay on top of those tires!
If you don't know how to check the tire wear indicators- look on the tire sidewall for either a small triangle pointing towards the tread or the letters "TWI". There should be several of them equally spaced around the tire on both sides. Trace your finger across the tire tread from the TWI and you should notice a slightly raised area in the tread grooves. Once the tire wears down even with the TWI you won't be able to pass a state safety inspection. There's the trick of using a (US) penny as an indicator by placing the penny headfirst into the groove. If you can see the top of Lincoln's head the tire has less than 2/32's of an inch left and is worn.
As your tread wears down to the level of the raised area in the groove your tire is also becoming less round and uneven. You should notice more resistance to turning, less comfort in the ride and handling and often a whine or hum particularly when leaning over. If you haven't maintained proper tire pressure or if there were minor tire imperfections these things will show up in the form of cupping or flat spots.
At any rate, you'll want to plan for your tire change in advance with whoever you use. The Dino's tires are a non-standard size and it's unlikely your local shop (or any shop if traveling) will have them in stock.
Hope I didn't ramble on too much!
Terran Sin
Chief Farkle Mechanic and Valet for Pebbles (formerly Sukuta Girl)