7 speeds is probably enough...
If you need a wider range, I would suggest a wider range 7 speed cluster rather than an 8, which may or may not have a wider gear range unless you search out a wide range cassette. When the manufacturers increase the number of sprockets it is usually set up to allow smaller changes between gears, not to give you higher or lower gears. For example, it is my understanding that you can currently get a 9 speed cassette with a wider range than is available in 10 speed (at least easily, I seem to recall reading in the forums that someone has a wide range 10 speed if you search).
Also, if the Brifters are not 8 speed, then you will have to replace them using another chunk of money... Seven speeds were made both as freewheels and cassettes, so you will have to ask which is on that specific bike... Either way, to upgrade you may need a new hub/wheel. With the upgrades you would probably be in the price range to buy a new entry level bike with zero miles...
As far as price, I just bought a 1988 Centurion Master Ironman (a fairly nice bike that cost about $800 back then) for just over $100, and it needs nothing but tires. It doesn't have brifters, so add a little for that (actually Brifters do cost a lot, so it MIGHT make the difference to some extent, but not $150+ worth)
If you like the bike the way it is, it may be worth it to you, assuming it is a fairly light lugged steel frame like mine... But, if your intent is to buy it and upgrade (other than minor stuff), you may be better off buying something else.
Although the above may sound negative, do not let it discourage you. If you like it, it fits you, it is reliable and will ride it, I think that any bike is worth $275...
Since it is from an LBS, ask if it includes any free tune-ups. That can make a difference too.
Good luck on your decision.