I have found 4202 mining truck for 17.49 and 4209 fireplane for 35.99. I looked it up here and they are CAGR -9.2% for the truck and CAGR -15.38% for the plane... Will this still be a good investment?

i just picked up 10 mining trucks at the same 50% discount from my local shopkos. at 50% off you will do fine. i have had good success with construction sets once they are a few years old. i passed on the fire plane though. no particular reason, other than fire and police sets don't get me too excited since they redo them every 2-3 years.

Yes thats where I found them - at Shopko

where are you located? i am in green bay, wisconsin. i also came across the star wars desert skiff on clearance for $14.99 (retail is $24.99) at my shopkos. i was able to get 9 of them. at that price it's a solid set, with great minifigs. might be worth your while if you find some in your area.

Plus you can get 10 dollars off coupon by email from shopko that works on clearance items.