Yes, they can, especially if you have more than one kit, bag or location to stock for emergencies. Certainly there are a few things that fall into the "can't have too many" category. Many other things, in excess, waste your resources and may even deprive you of an important, potentially life-saving item.
Having too many of an item that easily degrades or is actually unusable after the 'best by' date is the same as throwing money away. Having an inventory and rotation system can make managing your preparedness supplies easier and less expensive. These feed your preparedness shopping list and help you prioritize how to spend your preparedness funds (or help you answer the "what do you want for Christmas" question from your wealthy relatives!).
So what does that mean? The inventory is the actual list of items. Using a program like Excel or another spreadsheet, you can even list the locations of the items. Let's take "3-wick candles." It's good to know you have 4 of them, but if you can't find them when you need one, then you may as well have none. A physical copy of your inventory can provide that information when the electricity is off and evening is closing in: one each in the bottom drawer of both bathrooms, one behind the TV and one in the kitchen cabinet next to the mugs. Hopefully you have matches or a lighter taped to each, so maybe the listing becomes '3-wick candle with lighter.'
Your rotation system is, of course, how you manage and use those items with a defined shelf-life. Better to use them before they go bad and replace them than to throw them away. Examples of defined shelf-life preparedness items may include canned food or a variety of fuels.
How can these inventories make being prepared easier and less expensive? Have you ever been in that favorite store and thought "What a great special on these boxes of candles -- can't have too many!" Well, you could actually have too many. If you have 10 boxes with a dozen candles each, and you spent $10 on each, you have $100 invested in candles. If your preparedness plan indicates 4 boxes will provide the light you need for 2 weeks then you have $6 dollars tied up in candles you may never need. You may also have put off buying that solar wind-up radio because $50 seemed expensive. You could have bought the needed radio for what you have tied up in excess candles.
So your inventory list feeds another 2 lists: the WHAT WE NEED list and the DON'T BUY ANYMORE OF THESE lists. Yes, I keep a DON'T BUY list because I have favorite items that I tend to pick up, too. P51 can openers are my major weakness, and yes, you can have too many! Buying items with your preparedness dollars that are not on your NEEDS list will deprive you of something you acknowledge you need. Only you (or you and your spouse) can decide on what should be on the NEED list, which should also be prioritized.
Your inventories can also help you build kits for car or bug out bags that are either additive, or that have known redundancies. As an example, if you believe you'll most likely evacuate in your vehicle, then you may plan to only have 2 ways to start a fire in your car kit to go with the 3 ways in your GO bag. In my case, streamlining kits and GO bags based on the inventories allowed me to make room for some other items, such as a heavier sleeping bag in the car kit.
These techniques may not work for everyone, but as you build your supplies they should help. I can't think of anything worse that discovering after the emergency has started that you have too much of something but not enough of something else. In 1989 I stood on the roof of my building with neighbors on the evening of the Loma Prieta earthquake, watching the San Francisco Marina district burn. As we got ready to go back to our apartments, I asked if anyone needed a flashlight. To my surprise, 2 of the 4 couples told me they didn't have flashlights or batteries, just candles. They had never really considered the threat of post-quake natural gas leaks. I had a couple of spare flashlights and helped them out. Don't be like my neighbors were. Think ahead, know what you'll probably need. Know what you have and where IT is. Maybe you'll never need IT. Maybe you will and won't have a neighbor who can help you out when you aren't sure if you have IT or where IT is.