Does a JR pass or even a regional pass make sense for Kansai?

Note 1: Ishikawa is a prefecture, not a city. Its capital city is Kanazawa.

Opinionated note 2: Hiroshima prefecture is the most beautiful area in all of Japan. You do have to get out of Hiroshima city, however.

The usual answer is that you must add up the cost of all the train trips you plan to make (which you can look up for example on Hyperdia), and compare the total to the price of the pass. Some rules of thumb, however:

• The Icoca & Haruka package is almost always the cheapest way to travel to and from Kansai airport.
• If you limit yourself to Kyoto-Nara-Osaka-Kobe, a pass does not make sense.
• If you go to more distant places, then it is much easier to make a pass pay off. For example a round-trip from Kyoto to Kanazawa is almost 13,000 yen, so a Kansai-Hokuriku pass (15,000 yen) almost pays for itself.

It can make sense depending on your itinerary.

As you will be spending (what seems like) most of your time in Kyoto (and I assume staying somewhere close to the International Conference Centre) you may want to look into getting something like the Kansai Thru Pass 3-day ticket.

This grants you unlimited use of all services from...

Osaka Municipal Transportation Bureau
Kyoto Municipal Transportation Bureau
Kobe Municipal Transportation Bureau
Hanshin Electric Railway, Hankyu Railway
Nankai Railway
Keihan Railway
Kintetsu Railway
Sanyo Electric Railway
Kobe Electric Railway
Itami Municipal Transportation Bureau
Amagasaki Municipal Transportation Bureau
Takatsuki City Transportation Dept.
Osaka Monorail
Kita-Osaka Kyuko Railway
Nose Electric Railway
Hokushin Kyuko Railway
Kobe Rapid Transit Railway
Semboku Rapid Railway
Kobe New Transit
Keif*ku Electric Railroad
Hieizan Railway
Eizan Electric Railway
Keihan Bus
Hankyu Bus
Wakayama Bus
Wakayama Bus Naga
Shintetsu Bus
Kintetsu Bus
Kyoto Bus
Hankyu Denen Bus
Nankai Rinkan Bus
Nankai Bus
Nankai Wing Bus Kanaoka
Nankai Wing Bus South
Keihan City Bus
Kobe City Transportation Promotion
Keihan Uji Bus
Amagasaki Transportation Service
Hanshin Bus
Keihan Kyoto Kotsu

... but NOT JR Lines.

It also grants you discounts at certain shops along each of the lines.

Comparing the two options... (Adult Prices)
- JR Rail Pass (7 days) x 1   ￥29 110
- JR Rail Pass (14 days) x 1    ￥46 390
- Kansai Thru Pass (3-day) x 3 + (2-day) x 1
               ￥19 600 (5200 x 3 + 4000 x 1)

Note that if you get the JR Pass, you will at least require a return trip (of ￥580) if you are based in or around the International Convention Centre (as Kyoto Subway is not a JR Line) and intend to board JR services at Kyoto Station.

If however you decide you want to go further out than the main 4 Cities in Kansai (Osaka, Kyoto, Kobe, Nara) and go as far as Kanagawa, then as fkraiem said, getting a JR Regional Pass would be your best bet.

Also note that the JR Rail Pass must be purchased outside of Japan (at this point in time) whereas the JR Regional Passes can be purchased either outside Japan or within Japan (with a ~￥1000 price increase).

The Kansai Thru Pass is only available from within Japan. Further, the JR Rail Passes are all consecutive use (as in a 7 day pass expires 7 days after first using it regardless of how many times you have used in in those 7 days) whereas the Kansai Thru Pass is non-consecutive (using one day and not the next will still be valid for 2 more days (in the case of a 3-day pass).

In Summary

It really is up to your travel preference as to which routes you travel and how much time you have. Most of the time JR routes with be faster, though more expensive however they also cover a lot larger area. Getting a JR Pass may not be the cheapest option in all instances and will require an application before you arrive to Japan).

As @fkraiem states in the comments, over at Japan Guide there is a comparison of Kansai-centric fare paying methods which may help you make up your mind as to which would be the most beneficial to your situation.