Value is relative to purpose. If reselling is in your future, resale value retention is a consideration. If low cost, yet reliable operation in a business setting is a primary consideration, resale value is practically irrelevant.

In 2004, at the school portrait company I worked for, we had a choice. We could by Canon's excellent 24-70mm f/2.8 zooms for 330 cameras. At that point, the lowest price at which we could get them in bulk was just over $1000, which included a one year US warranty. But alternatively, we could get Tamron's excellent 28-75mm f/2.8 for $339 in quantity. The Tamron came with a six year warranty.

We would be using either of these lenses quite heavily! The average camera would be used for around 450 exposures per day, seasonally, for about 30,000 clicks per year, give or take 10,000. So they had to work.

The decision came down to price and warranty. We bought the Tamrons and never looked back. Our testing showed that the Tamron was just as sharp as the Canon at f/5.6 to f/8, the portrait aperture range we wanted to use on our APS-C Canons. It was noisier, but the application didn't require silence.

Some of those lenses were on their third or fourth camera body when our company division was sold to Lifetouch in 2011. VERY FEW ever required warranty service. A handful were repaired for drops or mistreatment (extreme heat from being stored in a car trunk in summer, or extreme cold from being stored in a car trunk in Minnesota winter).

We did have some photographers complain that they were not very sharp at f/16, and practically useless at f/32 (!), but that was because those photographers didn't have a clue about diffraction limiting of sharpness. They were group photographers used to small apertures on 8x10 view cameras! We had to educate them about depth of field calculators...

The newest Tamron 24-70mm f/2.8 VC lens is quite sharp, focuses quicker than the old 28-75mm, has excellent stabilization, and is MUCH better built than the lenses we were using a decade ago. It is also half the price of the newest Nikon 24-70mm f/2.8. Tamron still includes a six year warranty.

I have nothing against Nikon... I used Nikon (and Canon) cameras and lenses for 40+ years. But I'm also interested in economy. For about the price of the Nikon 24-70, you can buy the Tamron 24-70 AND their excellent 70-200mm f/2.8 VC zoom. I know what I'd do...

That 28-75mm f/2.8 we used so many of is still available for around $500. Used ones are around $275 to $300. I think they hold their value pretty well.