I know they are tempting, but that +20% army camp boost (or whatever reward you pick) doesn't add a whole lot on top of the 100% to 500% you likely have from advancements and/or artifacts.
In fact, the 20% from ad doesn't work the same way as boosts from artifact/advancement as it is applied after all other boosts are calcuclted (so in case described by you it's not 520% in total, but 600%). Also it can be 30% in later stage.