Getting back to the OP, "importance" is purely subjective. If you have need for appendages and are comfortable with and using them I suppose they would be important. Personally I don't much care for them. They have specific applications in Military and LE though they are not universally adopted. I have two handguns with a rail. My Walther P22 and my SiGPro 2022. If I had a choice in the matter I would go rail-less. I don't see the point or functionality from the perspective of my needs and uses.
I love everything else about my SP except the rail though there is no way to remove it so I just consider it a blem. It functions fine as is and as soon as it is completely broken in and has a set of TFO's on it, it'll be near excellence (I don't bellieve in perfection).
Ask yourself if you would be using the rail and with what accessory. That will determine it's "importance" to you and define your "need" one way or the other. Temper your decision making with these thoughts. If you do intend to carry with this handgun, will your accessory be mounted 24-7? If so finding a rig may be a bit of a challenge, even more so if you are going to be attempting a concealed carry. If you have a light or laser mounted to your rail, how much bulk and weight will it add when considering your CCW dressing options? In general, most people go with smaller/lighter choices when carrying for concealability aspects.
My very first handgun was and still is my P226. At nearly 19 years and over 20K rounds it has been flawless - and without a rail. I like the classic look as I've not been impressed with the "tacticool" look of things in recent years. I think the classics have a certain aire of style and good looks without all the "popular trending" towards useless appendages.
Looks aside, put your hands on as many of your "candidates" before you decide to buy. If the opportunity avails, put some rounds through them as well. Getting a feel for how the fit and feel in your hands will determine how well you may be able to shoot them. If it doesn't fit and feel comfortable, you will not shoot it as well as if it did. I have not been impressed by .40 in anything I've shot it through. Many like it for several reasons. I do not for many of my own. However, if you wish to shoot multiple calibers through the same handgun, the .40/.357SIG option for starters is the way to go. A 9mm and/or .22LR option can be gotten at a later time in the P226 or P229. There is also a .22LR kit available for the P220.
It is more expensive but if you choose a single gun for a single caliber and/or application, then you can't really go wrong with SiG, IMHO. Provided they fit and feel right in your hands, that is. They work for me and so that is what I own. I have tried many others and continue to do so when the opportunities present. The grip angle and ergos just feel right with the SiG's and have not with most everything else I've tried. This is something you will have to determine for yourself along with all the other things mentioned in this thread.
The Beretta Bobcat or Tomcat thing I cannot say much about as I've not had the opportunity yet. SiG does make the Mosquito which is described as 70% the size of the P226. It had some problems out of the gate, but most that have gotten them recently have had few bad things to say about it from my readings on various forums. It's a nice option to consider in .22LR.
Hope my input has been helpful.