Is this a good reason to delete cache?

Cached files reported means the OS is caching files to help improve the switching from app to app. Nothing to do with caches on the drive. Your computer is slow primarily because you are trying to run too many concurrent applications. The OS is being forced to use disk space for memory, which is much slower than RAM.

You need at least 8GBs of RAM. With only 4GBs you barely have room for one or two applications.

Ways to Help Make a Slow Mac Faster

1. 17 Reasons Why Your Mac Runs Slower Than it Should
2. Slow Mac Performance? This Article Solves It!
3. Fix slow start-ups in OS X | MacFixIt - CNET Reviews
4. How to fix slow shutdown and startup times. | MacTip.net
5. 6 Easy Tips to Speed Up OS X Yosemite on Your Mac
6. OS X El Capitan- If your Mac runs slowly
7. Visit The XLab FAQs and read the FAQ on Performance
8. Tips to Fix Issues that affect Mac Performance
9. Avoid using any third-party cleanup software. Usually, this software does more bad than good. You don't need it. All computers become slower over time even under normal use. Experienced users erase the hard drive and do a clean install from scratch from time to time; or whenever installing a major OS upgrade. Doing so means you must maintain regular and multiple backups.
10. If you have enabled iCloud Disk and are storing your Documents and Data in iCloud, then consider turning that off and signing out of iCloud. It can slow down the computer considerably. Please see the following from the user, fotomac: "The solution was to SIGN OUT of iCloud and my problem STOPPED! NO MORE SPINNING BEACHBALL! My computer's speed increased to what it should be and all my Apps now work!"
11. Add more RAM or cut back on the number of concurrently running applications and utilities. Remove unnecessary anti-malware software and any software that promises to clean your Mac. Check for runaway processes: Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity. Also, visit The XLab FAQs and read the FAQ on dealing with The Spinning Beach Ball of Death.
12. The Ultimate Fix: Backup everything, erase the drive, reinstall OS X, and restore your data from the backup. Reinstall third-party software from original media/scratch.

Caches are not the evil bane of Mac computers. They don't need your constant attention or a third party program to keep them 'clean'. Your computer has built in scripts to handle the 'cleaning' that's required and will handle that task perfectly well 99% of the time. The only time you need to be at all concerned about caches 'eating' up all your drive space are those rare instances when your computer crashes and upon startup the OS doesn't clean up after itself. If have to force quit my system, or if my computer loses power I'll generally do a safe start (hold shift until the apple icon appears) and then reboot normally. In a safe start the drive integrity is checked and cache files are deleted and trimmed.

Read Kappy's post again to understand how to speed up your computer. The only thing he doesn't mention is upgrading to an SSD but if you are using Mac OS 10.12 or later you definitely need more than 4GB of RAM.

I would either go to 10 (existing 2+new 8) or 16 (2x8)

You should check the health of your hard drive using DriveDX just in case it is contributing to your problems.

Its not uncommon to see apps use more memory with later updates.

Definitely agree with lllaass' suggestion on possible memory upgrades as it maximizes the amount of RAM for lowest cost especially if you find you need to max it out later. Just make sure to buy either Crucial or OWC RAM as Macs are very picky about RAM.

Yes I would delete the cache often. If you do not then it just keeps building up and eventually will start slowing down your computer. I try to delete mine at least once a month since that's how long it takes i've noticed before my computer starts slowing down.

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