The Tacoma/Mexico DV4 is semi-related to the Westerly DV4 in that it's an entry level, all solid wood, mahogany dreadnought. Hand rubbed finish and no frills.
THe Tacoma/Mexico DV6 has no correlation to any previous model. It's basically an entry level, all solid wood, rosewood dread. Hand rubbed finish and no frills
The Westerly DV52 and DV6 were basically Guild's midline dreads, and sort of Guild's equivolant to the vintage Martin D28 and D18 respectively. Quality dreadnought guitars, meant to have a vintage sound right out of the gate. In the late 90s, both guitars could be purchased for very fair prices, (as someone else mentioned) the DV52 was around $1100 and the DV6 was notably less. In my opinion, the DV6 is the most underrated Guild acoustic of all time. I've played a few (even a cedar topped one) and they were all exceptional.
The DV25 and DV4 are basically the same guitar, solid backed versions of the D25/D4. The DV25s have a gloss finish with a headstock overlay, The DV4s are hand rubbed with a silk screened logo. Entry level, few or no frills, all solid wood dreads. I have DV4 and it's a ridiculously good guitar for the price. It's super light (especially for a Guild), it projects well, and it's packed with mellow, mahogany tone. It's the best $400 I've ever spent on a guitar, that's for sure.
-Chris