I see no reason not to visit the Scott monument. For only £3 you can enjoy the great views the monument has to offer. I do recommend taking pictures on the highest level, since the views get better the higher you climb. Otherwise you'll end up with four equal sets of pictures. On the first level there's a room dedicated to Sir Walter Scott. During autumn and winter be sure to have a scarf and some warm clothes, since there's a really strong wind up there. If you're in Edinburgh, the Scott monument is definitely an attraction you have to visit.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.