What do you want to do when you're in Seoul?

Check out Ibis Ambassador Seoul Insadong, they're in that price range and are centrally located for tourism related to the historical palaces, Bukchon village, Ikseon-dong, Insa-dong all good for walking around as well as having some nightlife (Jongno-3ga station), restaurants, Cheongye stream, and Gwangjang Market (the netflix one only the nokdu jeon/pancakes are worth it there IMHO).

Ibis Styles Myeongdong - is mostly shopping which can be done during day and also not that far away but at night its a ghost town (besides the street food which isn't all Korean or that great) so you'll have to go towards itaewon since going further north will just be the business district as well.

Mondrian Itaewon - as the name suggests is in itaewon but off the main strip you have to walk a bit to get to that area which is the foreign district so if you want foreign food or shopping for larger size clothes, nightlife, and Namsan Tower (which is also not that far from myeongdong or insadong). Not much else right outside the hotel though. Also watch UV - Itaewon freedom the music video for a funny reference outside shots were filmed on location.

Mercure Magok - new but its location is only really good for being close to Gimpo airport other than that and a park nearby I'm not sure what you'd do there never been to much in that area besides the airport.

Ambassador Seoul Pullman - location is centralish and quieter but you will need to go across the mountain to get to Itaewon/Hannam or further towards Gangnam, or the other direction through downtown to get towards the historical stuff. Immediately around the hotel isn't too much besides a famous bakery called Taegukdang about 10 mins walk towards the station and nice park nearby.

Ibis Styles Gangnam - Close to Coex mall, and short ride to Jamshil area which contains Lotte world tower (tallest building in Korea), Lotte world amusement park (half indoors half outdoors) which all overlook the Seokchon lakes. For night life you will go to either Rodeo drive in Apku or Shinsa station. For any medical procedures, eyecare, skincare, etc all the main hospitals and clinics are in Gangnam in general. You'll be amongst newer tall buildings in a grid and expensive cars you'll understand the song Psy - gangnam style better haha.

I could expand further but it depends on the type of traveler you are and what you want to do. Also Seoul isn't a big city distance wise but still sometimes it can take 40 minutes to go like 5km if you hit rush hour or if there are protest blocking roads etc. You can avoid it mostly if you take the subway when possible but some of those hotel locations it might be easier to taxi around or if you're carrying a lot. Download Naver maps and you can plot it out ahead of time to see (google maps doesn't work well).

Upgrades wise I've only gotten one category upgrades as Gold or Platinum. Most of the breakfasts have quite a lot of vegetarian stuff but I haven't stayed at an Ibis in Korea, I'd check around for some pics of the spread.