Agreed. Assuming sufficient limiting and wide appeal things marketed at specialists/collectors can certainly do well though, e.g. DCC, Mo-Fi, Nimbus, Classic Records etc audiophile pressings. I have a fair few of those which are worth many, many multiples of their purchase price.
PS To keep the spreadsheet up to date here is where I think I am at present (everything that appears twice is correct, not a typo, I've just not combined as some were bought-in at different prices):
21304 Doctor Who £49.99
21303 WALL•E £39.99
10251 Brick Bank £119.99
75095 Star Wars TIE Fighter™ £169.99
75060 Star Wars Slave I™ £169.99
21306 Yellow Submarine £49.99 (I have two, but I've built one to keep so only counting one)
40222 LEGO Christmas Build Up £0.00 (freebie from Lego.com)
40222 LEGO Christmas Build Up £0.00 (freebie from Lego.com)
21050 Architecture Studio £138.97
75913 Speed Champions F14 T Scuderia Ferrari £79.93
75156 Star Wars Rogue One Krennic's Imperial Shuttle £0.00 (Tesco 3 for 2 offer with the two sets above)
75911 Speed Champions Mclaren Mercedes Pit Stop £21.97 (Amazon)
76052 Batman™ Classic TV Series £183.99 (Lego Black Friday)
40223 LEGO Snowglobe £0.00 (freebie from Lego.com)
40223 LEGO Snowglobe £0.00 (freebie from Lego.com)
10243 Creator Parisian Restaurant £128.37
21303 WALL•E £39.99
21304 Doctor Who £33.25 (Tesco 1/3rd off)
75150 Vader’s TIE Advanced vs. A-Wing Starfighter £39.99
75091 Flash Speeder™ £17.49
30446 The Batmobile £0.00 (freebie from Lego.com)
76046 Heroes of Justice: Sky High Battle £27.49
75140 Resistance Troop Transporter £29.99
30446 The Batmobile £0.00 (freebie from Lego.com)
21309 Saturn V £109.99
5004936 MF Cave Set D160 £0.00 (freebie from Lego.com)
Lego VIP Points discount applied to date -£50.00
Lego catalogue vouchers applied to date -£10.00
Total investment: £1391.36
Not counted in figures above but retaining some resale value (boxes, manual, packaging etc obviously retained):
Built 21306 Yellow Submarine (£49.99)
Built 40320 Volvo L340F Wheel Loader(£169.99)