Action Filters to only load data for certain action types

Question

I am relatively new to the MVC way of doing things and have run into a bit of a performance issue due to loading a lot of extraneous data in a base controller. I have read a bit about action filters and was wondering if anyone had advice on how to proceed. Here is my issue:

I have a Controller called RegController that inherits from a base Controller called BaseController. In the onActionExectuting method of the base controller I load several variables, etc. that will be used in a visible page such as viewbag, viewdata, etc. I only need to load this stuff for Actions with the result type ActionResult. In the same RegController I also have some JsonResult Actions that do not need all of this extra info loaded because they do not load a page or view template they only return Json. Does anyone have a suggestion how to handle this properly within existing framework features? Should I be putting these action in different controllers instead? I have many controllers with varying functionality split up in this same way and am hoping I can filter the action type versus moving them all to a JsonResultController or whatever.

Code (some of it pseudo) below:

public class BaseController : Controller
{
    protected string RegId;

    protected override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        base.OnActionExecuting(filterContext);

        if (filterContext.ActionParameters.ContainsKey("rid") && filterContext.ActionParameters["rid"] != null)
            RegId = filterContext.ActionParameters["rid"].ToString();

        Reg oReg = new Reg(RegId);

        // IF A VISIBLE PAGE IS BEING SERVED UP, I NEED TO LOAD THE VIEWDATA FOR THE PAGE
        SetViewAndMiscData(oReg);

        // IF THIS IS A JSON RESULT ACTION, I DO NOT WANT TO LOAD THE VIEWDATA FOR THE PAGE
    }
}

public class RegController : BaseController
{
    protected override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        base.OnActionExecuting(filterContext);
    }

    public ActionResult Page(string id)
    {
        // THE VIEW DATA SHOULD BE SET FROM THE BASECONTROLLER FOR USE IN THE PAGE
        return View();
    }

    public JsonResult Save(string id, string data)
    {
        // I DON"T NEED ALL OF THE VIEW AND MISC DATA LOADED HERE, INCLUDING THE AUTO LOAD
        // OF THE REG OBJECT SINCE I DO IT HERE FROM THE PASSED PARAMS.

        GenericResponseObject Response = new GenericResponseObject();
        Reg oReg = new Reg(id);

        if (!oReg.IsValid)
        {
            Response.Status = 1;
            Response.Message = "Invalid Record";
        }
        else
            Response = oReg.SaveData(data);

        return Json(Response);
    }
}