Since joining the forums, I've made so many "suggestions" for Kingdom Rush, the devs ought to be under deep hypnosis by now. I'll be updating this thread with my ideas as they come in from the netherworld.
Stuff I think would enhance Kingdom Rush:
An Open Love Letter to Kingdom Rush Fans Frequently updated!
The World's Greatest Kingdom Rush Sandbox Frequently updated!
Elite Hero skills Frequently updated!
Hero Towers Frequently updated!
The World's Greatest Kingdom Rush Challenge Editor
The Art of High Replay Value
Helm's Deep Endless Mode
Endgame Content
Endless Action in Endless Mode
Expanding the battlefield with scrolling
Hero Campaigns
Kingdom Rush Factions
Elite Challenges
Auto-Command Flags
Longer challenges for maxing towers and heroes
Hero-switching
Allow access off the road for heroes and reinforcements
Hero Suggestion: Kilele The Bard
Multiplayer Suggestion: Warpath
Multiplayer Suggestion: Crossfire
Multiplayer Suggestion: Tower-Terminator
Annual Holiday Content
User interface suggestions
Improving the AI for advanced towers
Save states for initial tower setup
hard mode gold standard
Other stuff:
The World's Greatest Kingdom Rush Level Editor
King Banesti's Emancipation Proclamation
Retro Campaigns
Updating Malagar's looks
Multiplayer Suggestion: Capture The Flag
Class-based Reinforcements
Meet the voice actors
Hero warning cry
You completed everything award!
A picture is worth a thousand words
Shadow Hero battles
Computer-Controlled Tower Challenges
The Fanmade Update
Cheesecake's name should be colored like cheesecake
Achievements and Milestones
Hire a PR person...for FREE!
Bundled Purchases
Hero Suggestion: Indiana James
Hero Suggestion: General José Artigos
Hero suggestion: Shadow
Product Placement
Cosmetic upgrades for max level heroes
Lore suggestions
Trolling attempts by the developers
Mode Suggestion: Pathfinder
Mode Suggestion: Counter Offensive
TF2 items for Kingdom Rush
The Platform Equality Comic