This info might be a bit late for some but might be useful for others.
I am from Penang, but been leaving in Melbourne for the past 8 years. I love traveling around and never get enough with Malaysia. Almost every year me and my husband (he is french) will go back to Malaysia and discovered new places to visit.
Now, to give some insight thought to your questions, I have been to Batu Caves 2 years ago, it’s a nice place to visit, and if you up to climbs the thousand stairs, but bare in mind that the weather is hot (can be up to 34’C) and humid so wear the right clothes. If you only have a short break in Malaysia, I think Batu Caves and Genting Highland for me will be at No. 9 places to visit out of 10. Genting Highland is a place if you love riding roller coaster and visit some casino. There are place to walk but it’s purpose is mainly for the casino and fun-fair like. So, it’s up to your interest.
I would recommend Cameron Highland if you like fresh air, walking and a little bit cooling places. I love Penang, partly because I grow up there, but mostly because Penang have a mix between city life and nature depending where you stay. There is a nice national park close to Batu Ferringhi ( we use to call it ‘The end of the world’), we went back a month ago, and had a wonderful time there. There’s beaches, and if you know how to find one, the you will get a nice clean beach to dip yourself in. If you like the city lifestyle, then stay in Georgetown area, close to Penang Road, you will get to see the busiest place in Penang around ChowRosta Market. Tanjung Bungah and Gurney area is also a nice place to visit if you like shopping malls and hawker style food. There’s hotels around there so you can shop till you drop and walk back to hotel.
If you like nature walk, then close by in the city there is a beautiful Botanical Garden, its quite big and lots of monkey. Rain forest fauna and Flora is very interesting. You can take a bus from Komtar to go to the Botanical Garden. There are many other places around Penang to visit but I think that will be enough for now. Ask me more if you like to know about other places in Penang and Malaysia.