Hello
Given that you are in the Hilton Charlemont, you could always walk to Ranelagh and then from there over to the RDS (via Marlborough Road and Herbert Park Road), it'll only add about 5 or 10 minutes to your walk and there's a great selection of restaurants in Ranelagh.
Marios - Italian, great food, does not take reservations though
Cafe Bar Deli - Mainly Italian but also other European-style food
Tribeca - best chicken wings in Dublin, burgers, salads and other dishes. would definitely recommend.
Ouzo - fantastic fish restaurant, has steaks also if you're not a fish lover
There are plenty of others to choose from. I would recommend using the website [broken link removed] - you can select the area (Ranelagh/Donnybrook/Ballsbridge would all be close) and type of cuisine, there are reviews included also. There is a new restaurant Maia in Ballsbridge which I haven't eaten in yet but have seen some good reviews.
Da Vincenzo or Canal Bank Cafe on Leeson Street also good.
Enjoy Bruce!