Compare apples to apples. Real property appreciates, tangible items depreciate. No, I would not buy real estate if it did not appreciate. I would rent and let someone else have all the headaches and up keep.
I think you are also confused about depreciation. In the cost approach you are working with today's (hopefully) costs and then adjusting for depreciation from all sources. In effect you are adjusting for age and condition combined. In the grid you can separate the two.
Think about it for a minute. Take a deep breath. Have you ever seen real estate go down other then temporarily? No.....it continually goes up in value, just ask your tax assessor.
If you are ask to provide a future value for something, you need to take into consideration both appreciation and depreciation that's why it becomes a complex appraisal assignment. Think about what they are asking you to do. Tell us what you think that property will be worth at some point in the FUTURE. Over all property values will, in all probability increase...if nothing else due to inflation. The improvement will have a certain life expectancy...probably much longer than the period you are considering.
So you have several different problems to solve. First how far into the future will you have to project. 3 yrs, 5 yrs, 10 yrs, 15 yrs, 20 yrs. You can base this on the life expectancy of the holder of the life estate. Say she/he is 65 now. You might then choose to use 15 years. Next how much will the value of real estate go up? Could be Zero, 3%, 5%, 6%, 8% or any number you might choose to use depending on your market. My market has consistently shown 6% to 8% per year on an over all basis. So, if you know the present value of the property...solve for each time increment using each possible inflation amount.
$100,000 today......6% appreciation compounded for say, 5 years would be, ahhhhhhh
$133,822 or say $134,000. You do that for every time period and every possible appreciation rate. You would also make the assumption the property is well maintained and keeps it's marketability. If you know what the value of the property is projected to be, you can also use the age/life method to determine the depreciation for that point in time.
I hope I am explaining this in a manner that makes sense to you. Remember, predicting the future is much more difficult to determine than a retrospective or current value. Disclaim, disclaim, disclaim.