I've gone the last few years and it is fantastic. And in my experience, most vendors price their stuff very fairly and haggling is abundant. My brother and I have gotten so many incredible deals over the years. Not garage sale/flea market $1 Earthbound bs but anywhere between 20-40% below or more ebay/vgpc value depending on who you talk to. And the vendor side is only part of it. The local barcade Ground Kontrol provides a ton of freeplay pinball and arcade machines, there are tons of old systems set up for freeplay (or test out your purchases from the vendors), there are contests and tournaments and also panels. Don't expect PAX level quality for panels and guests, mostly youtube personalities and local groups but this year they have the Angry Video Game Nerd and they've had ProJared, Game Sack, Metal Jesus, Pat the NES Punk and others in years past (and maybe again this year, not sure).
To address bikingjahuty's point about the resellers, there is some of that as well. Some of the vendors and retro stores are really shady. One store in particular "Retro Game Trader" is the worst offender. They have a booth set up about their store but don't actually sell anything at the expo. But they have people go around the expo and buy up stock that they turn around and sell at their retail store in Beaverton. Which if you've ever been there is the biggest joke of a retro store ever. I'm talkin' 2x-2.5x ebay for games. Super Castlevania IV for SNES loose priced at 89.99 kind of bullshit. Super shitty and every other vendor there hates their guts.
Portland is lucky that we have a lot of decent retro stores in the area (Except Retro Game Trader, seriously fuck those guys)
CD Game Exchange is by the best and most reasonable, they'll haggle up to 10% and usually their prices are below market already.
GameStar is generally overpriced but they often will do a 20% off purchases over 50$ or more so if you catch them sleeping you can get a deal or two. They don't really haggle though.
Videogame Wizards is super unorganized and often they don't price their games very well which you can use to your advantage. Which is how I scored a $50 complete copy of Klonoa for Ps1 last year. Haggling encouraged.
Another Castle (WA vendor) generally way overprices RPGs, (PS1 in particular) but the not as popular uncommon titles are usually priced reasonably and again, always haggle.
Those are the vendors I remember. There are so many others (a lot of Washington shops that I've never been to) and a lot of Mom and Pop and solo peeps with a table. Some people will be unreasonable but there are so many tables that it's hard to be upset.
I live in Portland so I'd probably recommend it to fellow Oregonians and Washington residents. Further than that, I don't know if it's really worth the drive/airfare hotel accommodations but if you are starved for retro gaming, this is a great event.
I'd be down for a VGCollect NW meetup. I don't really know a lot of retro enthusiasts irl so this would be a good opportunity. I just started law school here in Portland so I have to cut back significantly how much I spend this year but I'm still going to bring some cash and score some great deals.