I'm thinking you want to go with the "name brand" hotels, rather than one of the motels. Places like Holiday Inn, Wyndham, etc. There's a Portofino there (just east of the convention center, I think) that looks nice from the outside.
Previously, we really liked the Anabella, which is right on the corner of Katella and Disneyland Dr (next to Tiffy's). It's a "motel" but was very nicely appointed with some interesting room configurations. We stopped using them because of customer service (and walking distance - especially now with the parking lot closed off), but I understand they got new management a while back and things have improved.
Looking at
this map, I see a few things:
- Most of the "front" places on Harbor are motels and not conducive to a romantic evening.
- Fairfield Inn might be a good compromise between price and atmosphere.
- I see a Holiday Inn Express and a Residence Inn.
The more I look at it, the more I think that Paradise Pier might be a good choice...but that's for you to decide if the price just isn't right for you for this trip.